One tip. Use the trains.
I've been. Not with children though. As a student, with another female friend of mine.
It is intense, it is dirty, it is in your face, it is vibrant, full of life, MAD, it is the one country in the world I have been to where I got complete and utter culture shock (and I've travelled a lot!).
I've been to a lot of places for one month, or more, Far East etc.... and would happily have stayed longer. But, after my 3.5weeks in India, I was very much looking forward to getting home again.
I loved it. Loved the people. Loved the sights, sounds, experiences, nowhere like it, wonderful. But, I could not cope with a year. Too intense for me.
Having said that, I have friends who have moved to India, inner city, living pretty basic, and love it entirely and don't want to come home.
The one thing I would say- travel by train everywhere. They'll really see the country, and really meet the people. And don't travel first class, cos that's dull and they won't see real India that way! Even if it is cheap.
Wow. I wish them luck. (Sorry I cannot be more help!!)