Future working generation would be unable to support the retiring generation, creating an economic situation similar to Japan.
It's really a no win situation, as far as I'm concerned. Although I can not confirm, I bet that a strict one-child law might devastate millions of Indian families as they will not be able to support themselves. Also, like Uther said, the future economic situation would be a nightmare. The only real solution is a massive three way nuclear war between India, China, and Pakistan... forget I said that.
If you're answering from an authoritarian moral perspective, then yes. If from a libertarian moral perspective, no. I lean towards the latter, because people shouldn't be told how many kids they can have, I don't think. That said, the Indian people should stop having so many damn babies. There'd be more food and space to go around that way.