Although not funny to the posters who find this out the hard way; I do get a kick out of this when it comes up every so often. It is one of those policies most people wouldn't know, wouldn't care to know, wouldn't be expected to know until the time comes

however it is well documented and it is not limited to AA;

now for the value added piece to this thread (at least I hope it is)

go to the Travel with children forum and this is discussed and i think there are some possible work arounds