I am very impressed with the work of the Social Work and Research Centre ("SWRC", widely known as the Barefoot College) which was founded in 1971 in Tilonia, Rajasthan. http://en.wikipedia.org/wiki/Barefoot_College They have spread their work across India, Africa and Latin America.
Perhaps the two most impressive aspects of their work are their effectiveness and their avoidance of most forms of academic distractions. Somehow, each insuperable problem is made an advantage. Illiteracy and caste (Varna and Jāti) differences are solved by teaching using puppets. Gender discrimination is solved by teaching grandmothers.
What do they learn? They learn to solar-electrify remote villages all around the world. They train women because women stay. The women maintain the systems that they install and achieve higher status and become role models.
Perhaps the next stage in the development of the work of Barefoot College is the deployment in urban environments where you have the street children. Could solar electrification possibly coexist in higher crime areas where theft of centralized electricity is common? It's an entirely different problem that I do not know how to solve. When the Barefoot College effort began, they did not know how to solve their rural problem either. However, they were able to listen to the locals, who did know what to do and how. Perhaps this pattern can be replicated in the urban setting and a new solution can be created.
Have you contacted the Barefoot College and suggested partnering with a group of grandmothers in one of the impacted areas?
Better access to contraception in rural India and the slums? Like, maybe low-no cost condoms and easy access to birth control pills (but with 1 billion people, this second could have major impacts on water quality, so I hesitate on that one).
While I agree with the first two answers I have my doubts of how usefull the last one would be. Street children are resulted by people's poverty, not by having too many children. Poor people often depend on all incomes they can earn, and children at a very young age start to contribute to household income. As such people need many children free distribution of condomns or birth control pills would help not at all, as obviously people don't want to prevent births, but they want to have children, who early can contribute to household income.