My son is going to Auckland, New Zealand from Mumbai, India via Bangkok, Thailand with Thai Airways. Does he need a transit visa? His layover is 14 hours at Bangkok airport.
Assuming he is an Indian citizen, as long as your son stays in the secure area, he won't need a visa to transit in Suvarnabhumi.
Since he's flying with Thai Airways all the way, his luggage will be checked through. All he has to do is pass through security again, and go up to the departure level. And wait, a long time.
There are many restaurants and rest areas in BKK, so he won't really go hungry, and will have a place to sleep.