You could try ztk-babel client server game with chat
. It is not OO, (but should be). I wrote it to play with sockets and Tk. It has some valuable techniques, like using the nice Net::EasyTCP module, and integrating it with Tk. (The code works well, but can be hard to figure out at first, because of the depth and complexity of the hashes....my current attempt at the same thing, is using the same hashes, but making them OO, separating the players, and network stuff into separte namespaces.
It would be fun for them. It is a scrabble clone for 4 players over a network or LAN.. (Actually I made it to work like Scrabble, but became aware of the copyright infringements...so I made it so a random board is created for each game, and diagonal words count.
For something simpler, look at PONG with TkZinc