Actually, birth rates have been declining dramatically in India, with the majority of families having only one or two children, according to data released by the 2011 census. In this, India follows the typical pattern of developing countries, in which wealthier, more urban, and more educated parents tend to have fewer children than poor rural parents. There is a fairly straightforward economic explanation for this.
In an agricultural village, having many children ensures lots of hands to do chores and raise crops. As agricultural tasks require limited skills, children can start becoming economically productive at a young age. Urban, middle-class children, on the other hand, require many years of expensive schooling to qualify for middle-class jobs and do not become economically productive until their early twenties. It therefore makes sense only to have one or two children and invest in educating them. As access to food and medical care is better in middle-class enclaves, middle-class families do not need to have several children to ensure the survival of one or two to adulthood. Middle-class urban families are also more likely to have access to birth control, and educated women have careers they may not wish to abandon to raise many children.
Basically, rural families still have incentives to have large families and exist within a village environment with a tradition of gender inequality and large families, while more educated urbanites are moving away from this model. Women in many villages do not have access to birth control and may not have the option of avoiding early marriage and constant child bearing.