Little Man and Boo both have Tiny Love's Farm Animal Mobile at their respective cribs. Both love to watch the motion of the mobile, which I will say is oddly hypnotic.
I can't tell you how many times I've heard it cycle through Mozart, Beethoven and Bach. Each time at some point both babies fall asleep.
Some kids in primary grades fall asleep at story time at school. The sound of someone reading aloud is so deeply ingrained as part of their bedtime routine, that it triggers a sleep response. So, here's what I think. I'm training them to fall asleep when they hear classical music. Don't know if that's a bad thing or a typical thing.