a thinking game

I found this link on jenni's blog. It's in Japanese, but the directions are something like this:
1. All the people need to get across the river.
2. Only two people on the raft at a time.
3. The dad can't be alone with the daughters.
4. The mom can't be alone with the sons.
5. The robber can't be alone with anyone but the policeman.
6. Only the adults can operate the raft.
Try it out!