If possible, educational games should support more than one player. I don’t have any scientific data on this, but I am sure that a shared experience dramatically improves the learning. It is usually also more fun.
However, to protect the kids we don’t want to use any network communications. If the game should support multi-users, we need to do it on the same device. In our current case, this is not a problem since it is a turn-taking game.
No one likes to wait for his/her turn so it would be boring with too many players. I guess it should not be more than four players at the same time, but we support five, so the game should not feel limited.