I took French in high school, and have rarely found it useful.
However, if you learn French, Spanish or Italian, you can more easily decipher any of the other of those three because they are related. That is, of course, providing you can actually remember any of it twenty years later. I would recommend Chinese for the very young, based on my limited experience with my DD2 and the show "Ni Hao Kai-Lan"--she is picking up the inflections perfectly, which comes a lot harder as you get older. Same with Japanese. I have a patriotic aversion to teaching my kids Chinese on the basis that they will need it in the future--that speaks ill for the future of our country--but I suppose I'll probably get over it.
