The following link was emailed around work the other week. It's apparently used as an IQ test for job applicants in Japan.

http://freeweb.siol.net/danej/riverIQGame.swf

Click the big round button on the right to start.
The rules are:

• The father cannot be left with the daughters unless the mother is present.
• The mother cannot be left alone with the sons unless the father is present.
• The thief cannot be left with any of the family members unless the police chap is present
• Only the father, mother, and police chap can operate the raft

It is possible, but takes a bit of working out. Good luck! :)