Does this child have PWS?
If so, he will always feel hungry, no matter how much he eats. He will steal food, eat leftovers, eat out of a dustbin....
It isn't easy for any parent to say 'no' when a child is genuinely sick through feeling hungry, even though he has just eaten a large meal.
This hunger would keep him awake at night, give him tummy ache and have the syndrome has other effects, none of which are easy to deal with.
http://www.bbc.co.uk/health/conditions/praderw illi1.shtml