I mentioned that kids learn entire albums, but I think it is because they like entire albums.
Kids remember a lot, though. Over time, at least if they are like us, the great songs will linger in their memories, and the others will slowly fade away.

I don't think that songs don't last--I think that we rediscover them. There was a thread a while back about "Over the Hills and Far Away", a song I had not thought for a long while, but one that, on rehearing, is as moving as any song ever was.

It made me think of a line from an old Jimmy Durante song-"It's one of those songs that you think you forgot, but it's one of those songs you cannot".