I think Maxwell's Silver Hammer is in the "cartoon violence" category. Sort of like I used to know someone who wouldn't let her kids have toy guns that looked like guns, but toy guns that looked like Buck Roger's Space Blasters were fine.

When I had a small child I think I also would have excluded "songs that it will upset the grandmas to hear the kid sing," which would probably have ruled out, say, the Ramones' Beat On the Brat until the kid was old enough to fine-tune their behavior to be appropriate to the context.