I think the 3 toys rule works well. And teaching kids to put their toys away when they finish playing or as part of getting ready for bathtime/bedtime routine - that way you don't wind up buried under a mountain of toys but the kids can still play in the hub of the house and be involved rather than having to play in their rooms all the time. That said though, there are occasions when DD prefers to play in her room and that's cool too.