Given the range of evaluative techniques applied to studies in this review, findings are presented in four sections; the first two describing the study characteristics and quality, the latter describing the results of the meta‐analysis and realist synthesis.

A small majority of studies (57%) cited some theoretical grounding for their intervention (e.g. Social Cognitive Theory or Social Learning Theory). Theory‐based interventions appeared to be marginally more effective than those not referencing a particular theory (74% of those citing some theoretical background, and 60% of those citing none, were effective). Intervention duration ranged from 8 days to 12 months. Interventions were delivered by a variety of facilitators; community leaders (often selected for their cultural connection to participants), medical or healthcare staff, members of the research team or teaching staff. Interventions delivered by medical or healthcare staff appeared least effective. Seven studies evaluated the effect of remote delivery, of which 5 (71%) were effective. Education was provided in almost all interventions; other frequently applied intervention strategies included goal‐setting, reinforcement of positive health behaviours and role modelling.

Just over half of the included interventions were evaluated using a randomized controlled trial (RCT) or cluster RCT ( n = 27, 57%), and 8 (17%) were pilot or feasibility studies (of which 88% demonstrated positive results). Most studies were published after 2010 (68%), offering evidence of the contemporary nature of family‐based physical activity work, and alluding to the growing momentum of research in this setting. The majority of interventions were conducted and evaluated in the USA, but other study locations were included. Almost half of the studies included less than 60 participants and most (70%) included families with children aged between 8 and 11 years. Single‐sex interventions were uncommon; no studies focused on boys only, and only seven studies (15%) focussed specifically on girls (of which 86% reported a favourable effect). Studies targeting both sexes had broadly equal numbers of boys and girls. Studies including a majority of healthy weight participants appeared more effective than those reporting a high proportion of overweight or obese participants (80% compared to 59%, respectively). Approximately 85% of studies included short term post‐intervention follow‐up (≤3 months, n = 39), with 30% presenting results of a long term follow‐up (≥12 months, n = 14). Physical activity was assessed using subjective methods (questionnaires, recall diaries and interviews) in 25 (53%) studies, whilst objective assessment (pedometry, accelerometry and direct observation) featured in 22 studies (46%). Frequency of physical activity was commonly assessed using self‐report methods ( n = 21, of which 67% reported a favourable effect), whilst objective methods were used to record time spent in moderate‐vigorous physical activity or accelerometer counts per minute ( n = 16, 63% favourable), and step counts ( n = 7, 71% favourable). Overall, evaluations based on self‐report measures were no more likely to report a positive intervention effect (68%, compared to 64% of those using objective measures).

Forty‐seven interventions met inclusion criteria 28 , 30 - 74 (Fig. 1 ), of which 31 (66%) demonstrated a significant positive effect on physical activity. Table 1 provides an overview of included studies, grouped by study characteristics and demonstrating intervention effect. Further details on each of the studies, including a description of the intervention and the evaluation used to assess effectiveness, are provided in Supplementary Table 1.

Supplementary Table 2 presents the results of the individual item and overall scores of the quality assessment. ‘Study design’ was the item upon which most studies (72%) were deemed ‘strong’, followed by accounting for confounders (57%), withdrawal and drop‐out (57%) and data collection methods (43%). Issues of selection bias (e.g. sample representativeness of target population), and participant blinding were inadequately addressed; only eight and four studies respectively received a strong rating for each of these criteria. Overall, only three studies received a ‘strong’ rating (6%), 21 were rated ‘moderate’ (45%) and the remaining 23 were rated as ‘weak’ (49%).

Nineteen studies, one of strong 74 , ten of moderate 30 , 35 , 41 , 47 , 53 , 58 , 67 - 70 and eight of weak methodological quality 28 , 39 , 45 , 50 , 51 , 56 , 63 , 65 provided sufficient data to be included in the meta‐analysis. Of these, 15 were included based on published data, four on author‐provided data. Other studies reported only graphical information, or did not provide sufficient data to calculate a post‐test mean and standard deviation for each group and were therefore deemed unsuitable for inclusion (these presented, for example, change in pre‐post scores between groups, geometric mean and interquartile range, ‘difference score’). The pooled analysis (including 715 control and 863 intervention participants) showed a statistically significant effect in favour of the intervention groups (standardized mean difference 0.41; 95% CI 0.15–0.67; p < 0.000) (Fig. 2 ); this is deemed a small effect size 27 . The I 2 value was 83.5%, indicating high heterogeneity 75 . Given the weight and magnitude of effect demonstrated by one study 47 , sensitivity analyses were conducted to assess the impact of removing this study from the meta‐analysis. In this moderate‐quality study, families received educational materials on the benefits of physical activity, and information about available weekend outdoor activities and pedometer step targets. When this study was removed, the effect was reduced (standardized mean difference 0.29, 95% CI 0.14, 0.45), and the heterogeneity decreased to 45.6%. No sub‐group analyses for type of physical activity measure or study quality were conducted because of lack of heterogeneity (only four studies used a self‐report measure, and only one received a ‘strong’ quality rating).

Realist synthesis

Although all 47 studies were potentially eligible for inclusion in the realist synthesis, only 28 provided sufficient information to describe outcome patterns (defined as being of adequate ‘relevance’ and ‘rigour’ 26, 29) and hence contributed to the realist synthesis 31, 33-36, 38-41, 44-47, 49, 51, 52, 59-62, 64-66, 68-70, 74, 76, 77. These studies displayed great variation in the context within which interventions were conducted, the intervention strategies employed and the (implicit) mechanisms targeted. Despite this heterogeneity, the realist synthesis enabled extraction of demi‐regularities (outcome patterns). The final programme theory demonstrates these patterns (see Fig. 3), illustrating configurations supported by evidence (or hypothesized based on evaluations). Specific configurations of interest are discussed below (see Fig. 4).

Figure 3 Open in figure viewer PowerPoint Final programme theory for family‐based physical activity interventions. (1.) Solid arrows indicate configuration between context, mechanisms and outcomes evidenced by the included studies, dashed arrows depict those configurations that were hypothesized but not evidenced. (2.) Arrows are labelled with the studies that have informed them: A: ABC; B: Aventuras Para Ninos; C: Reach Out; D: SHARE AP Action; E: Family Connections; F: Healthy Choices; G: HIKCUPS; H: Rhodes; I: Growing Healthy Families; J: Healthy Homework; K: TEAM; L: A Family Affair; M: Hovell; N: Finkelstein; O: Centis; P: Healthy Dads, Healthy Kids; Q: ABC (internet); R: One Body One Life; S: GEMS Memphis; T: Chen; U: Triple P; V: MEND 7–13; sVb: MEND 5–7; W: Fit for Health; X: Arredondo; Y: De Bock; Z: C‐PET; 1: Fit4Fun. (3.) Grey text indicates those items that were hypothesized (during the initial programme theory development phase) to be of interest, but were not supported by evidence from the included studies.

Figure 4 Open in figure viewer PowerPoint Overview of main patterns identified in realist synthesis of family‐based physical activity interventions. (1.) Solid arrows indicate configuration between context, mechanisms and outcomes evidenced by the included studies; dashed arrows depict those configurations that were hypothesized but not evidenced. (2.) Arrows are labelled with the studies that have informed them: A: ABC; B: Aventuras Para Ninos; C: Reach Out; D: SHARE AP Action; E: Family Connections; F: Healthy Choices; G: HIKCUPS; H: Rhodes; I: Growing Healthy Families; J: Healthy Homework; K: TEAM; L: A Family Affair; M: Hovell; N: Finkelstein; O: Centis; P: Healthy Dads, Healthy Kids; Q: ABC (internet); R: One Body One Life; S: GEMS Memphis; T: Chen; U: Triple P; V: MEND 7–13; Vb: MEND 5–7; W: Fit for Health; X: Arredondo; Y: De Bock; Z: C‐PET; 1: Fit4Fun. (3.) Grey text indicates those items that were hypothesized (during the initial programme theory development phase) to be of interest, but were not supported by evidence from the included studies.

In the context of family constraints (such as time or scheduling difficulties), a combination of goal‐setting and reinforcement intervention strategies was effective in changing physical activity behaviour, through the mechanism of increased motivation (see Fig. 4a). Behaviour change theories, such as the Theories of Reasoned Action and Planned Behaviour 78-80, and the Health Action Process Approach 81, suggest that goal setting behaviours (e.g. thinking through realistic and/or preferred outcomes) increase motivation and promote intention formation. For example, effective family‐based goal‐setting interventions included the study conducted by Rhodes and colleagues 59, which focused on family planning for physical activity. Families were encouraged to plan for ‘when’, ‘where’, ‘how’ and ‘what’ physical activity they would undertake using a provided family calendar and workbook. The authors hypothesized that common barriers (such as perceived limited time available for physical activity because of work or domestic duties 82) may be overcome by increasing parental motivation (Study H, Fig. 4a). Goal setting may provide busy parents with the additional impetus needed to prioritize their child's physical activity above other competing demands. In addition, parents in one pedometer‐based intervention where weekly telephone calls were provided to reflect on progress and encourage greater engagement in changing behaviour were reported to appreciate the systematic reinforcement they received 38. Authors hypothesized that the praise provided during telephone calls encouraged parents to change their physical activity behaviour (and that of their children). This observation is congruent with Self‐Regulation Theory, which suggests that motivation may be increased through observing discrepancies between actual and desired behaviour, a process in which self‐monitoring plays an important role 83.

Our findings suggest that providing education is an effective intervention for changing physical activity knowledge, particularly in the context of a lack of understanding of how to change child physical activity behaviour, and where resources for child physical activity are inadequate (see Fig. 4b). Focus groups, conducted by Arredondo and colleagues to inform intervention development, highlighted parent's lack of knowledge and access to resources 73. The resulting intervention provided weekly information sessions designed to educate mothers and daughters on healthy behaviours. However, this and other studies confirmed that education alone is unlikely to change behaviour 35, 41 (Study X, Fig. 4b). Parents in the C‐PET intervention suggested that providing health information in combination with reinforcement (such as a reward chart to recognize increased walking) was more effective 70 (Study Z, Fig. 4b). Future efforts should therefore focus on providing feedback or facilitating self‐monitoring (particularly to increase physical activity awareness) to enhance the effect of education.

Most interventions included in this review targeted more than one health behaviour (e.g. physical activity and diet), but we did not identify evidence to either support nor refute the effectiveness of this strategy (as compared to targeting physical activity only). However, focusing an intervention on something other than the health benefits of physical activity or weight loss appeared to be an effective mechanism for changes in physical activity (see Fig. 4c). The ‘Healthy Dads Healthy Kids’ intervention was marketed as an opportunity for fathers to spend quality time with their children 69. The programme successfully used physical activity as a medium to engage fathers in play with their children, rather than as an explicit strategy for weight loss (Study P, Fig. 4c). Similarly, a parent‐focused intervention that facilitated shared ideas on active transport, ‘lifestyle’ physical activity (e.g. gardening club), promotion of outdoor activities (e.g. forest trips) and reducing obesogenic traditions (e.g. healthier birthday parties), suggested that the character of the intervention as ‘fun’ and ‘childlike’, rather than ‘good for health’, may have contributed to its efficacy 76 (Study Y, Fig. 4c). Other evidence suggested that this strategy may be particularly useful in the context of those with low self‐esteem or poor body image. The ‘HIKCUPS’ intervention did not focus on weight loss (despite being aimed at obese children), but instead focussed on improvements in motor skill proficiency and perceived physical activity competence as alternative benefits 42 (Study G, Fig. 4c).

The focus on the development of movement skills in HIKCUPS 42 is hypothesized to have impacted on the children's confidence to change their own physical activity behaviour (see Fig. 4d). Children's confidence (identified as both a mechanism and an intermediate outcome) is further suggested to have a bi‐directional relationship with physical activity, as evidenced by the Reach Out and Healthy Choices interventions 36, 52. Healthy Choices focused on building cognitive and behavioural skills to support physical activity, with learning experiences designed to improve perceived competence in a supportive environment 52 (Study F, Fig. 4d). Whilst it was not possible to clearly identify the underpinning mechanism(s) for the relationship between confidence and behaviour change, it is consistent with the Social Cognitive Theory, which asserts that behaviour is directly influenced by self‐efficacy (people's belief in their ability to perform a specific action that is required to attain an expected outcome) 83.

Consistent support was found for changes to the family psycho‐social environment as a target for intervention for positive changes in physical activity behaviour, either directly 28, 34, 38, 39, 45, 46, 66, or via the child as the agent of change 64, 84 (see Fig. 4e). The C‐PET intervention targeted modifications of the family environment, and the importance of family support for physical activity was emphasized throughout 70 (Study Z, Fig. 4e). Authors describing A Family Affair report that an improved daughter–mother relationship led to greater support for a healthier lifestyle, namely via co‐participation in physical activity 34. This intervention included family celebrations to further emphasize the role of the mother–daughter relationship (Study L, Fig. 4e). The One Body One Life intervention asserted that physical activity choices made by family members will positively affect the home environment, and may subsequently make it more conducive to behaviour change 66 (Study R, Fig. 4e). Family Systems Theory supports this notion; it suggests that an individual's functioning is integrally tied to the functioning of other family members, which may lead to complementary patterns of behaviour 85. A virtuous cycle (in which complex chains of events reinforce themselves through a feedback loop) may occur when one family member becomes more physically active, prompting others to follow and engage in activity themselves. However, whereas this may impact on increase family co‐participation in physical activity, the effect on child physical activity may be limited because of displacement (e.g. children replacing physical activity after school with family dog walks), as suggested in C‐PET 70.

It is also important to note that, conversely, a lack of family support may restrict healthy behaviour change. The process evaluation of the Fit4Fun intervention highlighted that children commented that their ‘parents did not really encourage [me] to do the physical activities’, and hypothesized that poor family engagement may have contributed to the only modest improvements in physical activity outcomes 74 (Study 1, Fig. 4e).

Both Choices 64 and Healthy Dads Healthy Kids 69 cited the child as the agent of change (see Fig. 4e). For example, Healthy Dads Healthy Kids taught children to role model and encourage their fathers to adopt healthy behaviours, resulting in a significant change in both child and adult physical activity levels 69 (Study P, Fig. 4e). Further, authors of Healthy Homework report that intervention tasks were designed to foster family involvement, with the intended side effect of improving relationships and promoting healthier lifestyles throughout the family 45 (Study J, Fig. 4e).

The way in which the intervention was delivered was suggested to be important for engagement and efficacy (see Fig. 4f). Three different contexts for intervention delivery were identified. Evidence suggested that interventions tailored to the ethnic context within which they are delivered were well‐received (e.g. adherence to study protocol, engagement in intervention) 28, 31, 36, 86. The Reach Out intervention team took particular care to incorporate cultural characteristics from the African American community (the target group), adjusting the protocol to fit with language, food and activity preferences expressed by participants in formative qualitative research 36 (Study C, Fig. 4f). The importance of cultural relevance is further highlighted by Aventuras Para Ninos 28. The inclusion of Latino promotoras (health advisors who attended family homes to offer educational material and assistance with goal‐setting) was cited as critical to maintaining adherence to the intervention (which was targeted at Latino families) (Study B, Fig. 4f). Similarly, information provided by Chen and colleagues in an effective play‐based educational intervention was written in both Chinese and English, and delivered by bilingual counsellors 86 (Study T, Fig. 4f).

In addition to ensuring cultural relevance, Newton and colleagues suggest that targeting the whole family may be an effective strategy in increasing intervention adherence 77. Reflecting upon the pilot data from the P‐Mobile intervention, in which one parent and one child set goals for increasing their step counts, they state ‘that interventions could be strengthened by engaging both parents and incorporating siblings into the intervention’ (p11). Further research is needed to elucidate the impact of wider family engagement.

Rhodes and colleagues discuss the need to understand the specific barriers to physical activity experienced by target families before designing or evaluating an intervention 59. In a review of parenting that informed their later physical activity planning intervention, they report time constraints as most detrimental to health promotion 82. The synthesis identified two differing approaches to addressing parents' perceived lack of time (see Fig. 4f). The first focusses on facilitating social networks between families in the context of a participatory group‐based intervention 76. Parents were pleased that they were able to share project responsibilities, reducing the individual burden without compromising the efficacy of the intervention in increasing physical activity in their children (Study Y, Fig. 4f). In contrast, Chen and colleagues describe a mail‐based programme designed for time‐poor families, suggesting that the delivery of educational materials direct to family homes (therefore eradicating the need for families to schedule in intervention sessions) was effective in ensuring intervention adherence 86 (Study T, Fig. 4f).