Could also connect a bunch of locks and put all the keys on a key ring. Lots of pictures of latch, lock, etc ideas for montessori type preschool. This lock one could be made with 2 boards, some o-rings, and some locks from Dollar Store.
"This is something I just started for my two year old who is thriving at the moment and learning everything like a little sponge! I learned a few tricks working at a day care :) you can get posters and other learning things from the dollar tree"