I have worked in class rooms from kindergarten to high-school and I have not seen a child over come these type of locks. (To be fair I have never seen them beyond 1st grade classrooms). I found this article on magnetic locks:
http://united-locksmith.net/blog/eve...magnetic-locks
It is a lot of info, but it talks about magnetic keyed locks (like this one). It is not super high security, but it will work for children no doubt. It is the most uncomplicated form of magnetic locks, but the cons section in the article said that the only real downside is the security it offers. If it does offer ok security against a criminal, so that would make it super effective for young children.
Again I have seen these locks work in a classroom setting, with up to 40 kids running around pulling on the doors. I have yet to see the lock fail.
I hope that helps.