I have to say that decorating a childs room is proably the most fun rooms in a home to decorate. There are alot of different things that you can do in these rooms that you normally wouldnt do through out your home.
Right now my daughters room was just redone. She wanted a variety of different colors on her walls, which she used her hands to paint hand prints every where. It came out rather nice and she loves it which matters the most. So now she has splotches of hand prints on her walls in black, orange, yellow, pink, blue and green
As for my son, he also redid his room. He wanted black walls which he then took fluorescent paints and painted peace signs and other message all over the walls. I personally dont care much for it, but he seems to love it. Though as soon as he heads off for college I know Ill be in that room with some primer and a much lighter color!!
These are great ways to allow kids to express themselves in their own private way. They of course also enjoy doing the work of making their rooms, more their rooms.