The problem-I work at a busy suburban library location with one reference desk. One summer, it seemed that we were constantly in the children's room picking up puppets, books, etc. While this needed to be done, if we spent all of our time cleaning, it took away from other duties, such as planning for programs and ordering books.
Our solution-we bought a bunch of stickers through Smilemakers when they were on sale. Then, we hung signs in the children's room that ask kids (and parents) to pick up the puppets and books when they were done playing with them. We tell them if they clean up, then they should stop by the reference desk to pick out a sticker for helping.
The result-I was pleasantly surprised at how well this worked. We now have a steady stream of kids (usually ages 2-6 years) coming up to the reference desk to ask for their stickers. Staff still has to pick up the children's room, but nowhere near as much as that one summer. As an added bonus, staff get to interact with kids who don't normally come up to the reference desk and the kids learn how to talk to adults and ask for what they want. It has turned into a good in-house p.r. move.