Every now and then I hit upon something that I know is a good idea. And, though this doesn't happen very often, this is one of those times. There's no way around it: decorating your kids' rooms with their help is a great opportunity for you and for them. Oh, I know there are lots of little bugs in the idea and potential complications--but that doesn't change the fact that it's a good thing to do.
Taking a room that was decorated with younger kids in mind and turning it into "hip, way cool pad" is a great way to let your kids know that YOU know that they're growing up. Taking down the wallpaper borders of stuffed bears and turtles and replacing it with something more age-appropriate will make your kids feel important. And involving them in that process, seeking their input and listening to their suggestions will make them feel that they are on the path to growing up--they're actually an active force in the creation of their new room.