A game of cricket is beginning in the migrant community of Bakkarwala, Delhi. The sun is blazing and the ground sodden from months of heavy rain, but the children burst onto the field with barely contained excitement. The session's young facilitator, Pradeep, leads them in a catchy Hindi energising chant.

"You're not loud enough," he cries. "You need to shout." The resulting roar echoes off the run-down tenements and attracts some local youths – this is their space and they're curious.

This is a Street20 cricket session for urban spaces, delivered by Magic Bus, an NGO that mentors children and adolescents through sport. Working across India to communicate development messages on health, education, and gender, Magic Bus has been active in Bakkarwala since 2011, and currently reaches 1,600 children in this marginalised community.

The activity's theme is health and, after a session on cricket technique, the key message is delivered by a game of dodgeball. The "healthy" children dodge the balls – the "disease" – defending themselves with their bats, the "soap". The message may be simple but for many of these children it is new.

As play commences, another story begins to emerge. There are more than 30 children here but less than a third of them are girls. Of the 20 young Magic Bus leaders, only one is female.

According to Dasra, a leading strategic philanthropic foundation, adolescent girls comprise around 11% of India's population. Yet this estimated 113 million people have little influence over their own health, relationships, education or future. They are India's invisible population.

Unicef considers adolescence "an age of opportunity", but according to Vacha, a Mumbai-based women's group, it is when a girl's world contracts. This is the time when young women face domestic confinement, exclusion from education, and preparation for the traditional roles of wife and mother. Central to this, says Amrita De, project co-ordinator for Vacha, is the absence of government policy relating to this population.

"Adolescent girls do not really exist in India's policy framework," she explains. "They don't fit into the population of children because they have different needs [from boys], but they are not yet women. Government schemes only see them as girls who are about to be mothers."

Safety concerns

Back on the streets of Bakkarwala, the story unfolds. This is a community on the verge of change, where on the face of it the principle of equal opportunities for girls and boys is beginning to be recognised. But there is a growing problem that is further reducing girls' mobility and threatening to undermine development efforts.

"I'm worried about safety," says father-of-three Ramkishan Gautam, prompting an affirmative murmur from his neighbours. "I want girls to be allowed to learn and leave the house but crime against them has increased. They are vulnerable."

This is a story told time and again throughout Delhi and Mumbai. There is a significant rise in reports of rape and Eve-teasing – sexual harassment of women and girls on the street. As a result, fear is now threatening to paralyse communities and further erode freedoms.

This has potentially more far-reaching consequences. "Take early marriage," explains Havovi Wadia, head of research and development at Magic Bus. "In slum communities, where accommodation is insecure and both parents work, girls are vulnerable when they return from school. Early marriage is one way of keeping them safe."

In the face of what is described by Dasra as a deep-rooted patriarchy, empowering adolescent girls is crucial. It also makes economic sense – enabling young women to remain in education, and delay marriage and pregnancy, has the potential to add $110bn to the nation's GDP, according to Dasra's report, Owning Her Future: Empowering Adolescent Girls in India.

Addressing the third International Forum on Sport for Peace and Development earlier this year, United Nations secretary-general Ban Ki-moon remarked that sport for development "can and must play a significant role in gender empowerment". In addition, the UN Taskforce on Sport for Development and Peace acknowledges the potential of sport to help achieve development goals.

Pratik Kumar, CEO of Magic Bus, says it is particularly effective in engaging young people. "It uses the magnetism, the power it inherently has, to attract children and youth to deliver development messages. It is subtle and fun and nobody feels preached to." He adds that sport attracts and retains volunteers, making programmes more sustainable.

Organisations like Magic Bus are working throughout India to provide safe spaces for girls to play alongside boys, increasing their visibility within communities, challenging gender stereotypes and demonstrating capabilities beyond their socially assigned roles. "Boys are genuinely shocked when they see what girls can do," says Wadia. "If they're not raised that way, how would they know?"

Such programmes might also be the only access a girl has to information about her sexual and reproductive health, a taboo and little-discussed subject within many Indian households, yet crucial to a girl's health and awareness of choice.

But sport for development is not without its challenges. Space can be a problem in urban districts and there is the issue of ensuring the needs of the most marginalised are met. This is a particular difficulty in poor or conservative communities, where sport is considered a luxury, or where girls are prohibited by religious law from playing alongside boys.

Yet while "behaviour change takes time", according to Kumar, progress is evident. In the two years since Magic Bus established its Bakkarwala programme, there has been a ninefold increase in the number of girl participants, and 26 female community youth leaders have been identified for training.

"One of the simplest ways of ensuring that the current and next generation is going to make a different future for themselves is to get the girl child inspired," says Kumar. At close of play in Bakkarwala, it seems there is hope for India's girls.