How long should women take off from work after having a baby? It’s a charged question. Scandinavians think women should have a lot of time; Americans seem to think women need little or no time at all. At the heart of the question is the effect on children: Does it help or hurt them to have a parent at home?

But attempts to study it scientifically have produced maddeningly complex results.

One study found that children from better-off families faced cognitive and behavioral setbacks when their mothers returned to full-time work within nine months of childbirth. But in another, children of poorer women (pdf) made both academic and behavioral gains, on average, when their mothers returned in that timeframe. Other research has come up with mixed findings (pdf).

Since some of those studies were done, however, the world has changed. More women work, and are making more money. Child care has improved, as the importance of early childhood development has been recognized. And fathers are getting more involved in it.

So a pair of researchers delved into more recent data—children born in 2000 and afterward—to ask the same question: do children suffer, academically and emotionally, when women go back to work quickly?

The answer, almost always, was no.

Caitlin McPherran Lombardi of the University of Connecticut and Rebekah Levine of Boston College published two studies on Dec. 19—one, in the journal Child Development, about children in the UK and Australia, and one, in Developmental Psychology, about American kids. The studies followed children and families from birth until they entered primary school. What they found: “There wasn’t any negative link between returning to work early and children’s development, both in terms of academic and behavioral skills,” Lombardi says.

To be sure, there were some caveats. In some cases, children of poorer mothers in the US fared better when the mothers went back to work early. This could mean that the mothers’ extra income helped offset other downsides. In other instances, children from better-off families suffered slightly when their mothers went back to work earlier. Both these results appear to support prior research findings.

Another caveat was that in some cases in the US—but not in the UK and Australia—children were more likely to misbehave in kindergarten if their mothers had taken less leave. Kids whose mothers returned to work part-time between 9 and 24 months after childbirth had higher rates of conduct problems in kindergarten (as reported by teachers) than children whose mothers had stayed out of the work force for at least 24 months. Lombardi hypothesizes that the reason this pattern only shows up in the US may be that part-time work in the US can be more stressful, as it tends to be lower paid and without benefits, while part-time work in the UK and Australia is more often of higher quality.

But taking these variations into account, Lombardi and Levine’s broad conclusion for the various cohorts of children was that the length of maternal leave really didn’t matter much.

What makes this especially surprising is that the three countries they tested have very different attitudes to parental leave. The US has no federal paid maternity leave policy, and allows for only 12 weeks of unpaid leave—and even for that, the bar for eligibility is quite high. In the UK, the study says, women’s jobs are protected for 39 weeks after childbirth, with the first six weeks of maternity leave at full pay. In Australia, mothers can claim up to 18 weeks’ leave, paid at the national minimum wage.

All in all, this suggests that parental-leave policy makes more of a difference to women’s ability to keep their careers than it does to their kids’ development. US mothers go back to work soon after childbirth, most of them full-time, but a lot subsequently drop out. Women in the UK and Australia come back slowly, and part-time, but then are more likely to stay in the workforce. Women’s labor-force participation in the US has been falling behind that of other OECD countries, and research has shown that differences in parental-leave policies are partly responsible (pdf).

All this suggests that making it easier for women to not sacrifice careers for children is good for their families in the long run. “There’s not a lot of association between early employment and children’s development and so policies that encourage moms to be able to stay in the workforce, and in their careers during the period of childbirth and having young children, those would support the longer-term ability of mothers to provide income and other human capital may benefit themselves and their families,” said Lombardi. Yet another reason why the US needs to reconsider its shameful backwardness on parental leave.