Upvote:1
Air India has this page:
http://www.airindia.in/documents-to-carry.htm
Which says that school ID cards are fine for children. I found similar language in many other airlines' websites (eg: Air Asia - http://www.airasia.com/in/en/about-us/terms-and-conditions-i5.page). Seems like school ID cards are fine in India for domestic travel.