What goes on the walls before semi gloss paint to prevent peeling?

We just recently had a friend paint our bedrooms and bathroom. One side of the bathroom wall started peeling. My six year old helped the process along but I have got that area totally peeled and prepped to be painted again. But what do I paint the wall with or prep it with before I put on the off white semi-gloss paint so it will not peel again?What goes on the walls before semi gloss paint to prevent peeling?
Depending on the type of surface to be painted, I would recommend either a wash with T.S.P. or denatured alcohol (be careful about the fumes). Rinse with a damp cloth and let dry thoroughly. Then primer coat the wall with Kilz stain-blocker, let dry 24 to 50 hours and paint away.What goes on the walls before semi gloss paint to prevent peeling?
primer. And be sure you get paint made to be in damp areas. this is very important. Talk to your local paint shop guy, they should be able to set you up right.