I’ve had two “only children” in many ways - my son is 15 and my daughter 2, and music is one of the biggest shifts I’ve seen in early childhood fashions. When my son was a tot, it was all Barney and Raffi, all the time. Clearly “kid music” with upbeat tempos, bright cheery vocals and not the sort of thing a parent could listen to exclusively without a rifle and a clocktower.
When Amazon wishlisting for my daughter, I found a lot more options. Raffi’s still around, of course, and his current successor is The Laurie Berkner Band, but there are CD’s put out by rock bands - Greenday’s songs have been rewritten into a “children’s CD”. Jerry Garcia and his buddies put out at least one children’s CD before he died. There are CD’s of high quality fully orchestrated classical music - Mozart, Brahms, Beethoven, et al. put out specifically for children. There is a great series of Lullaby CD’s from around the world: one is Brazil, one is Celtic, one is African, etc. - and these are compilations not of “children’s music”, but of real music that is appropriate to fall asleep to.
And beyond the general increase in quality of CD’s marketed at children or parents of infants, there also seems to be a general increase in the notion that it’s okay to just listen to what you like and expose the kids to “grown-up music”. When my son was an infant, he listened to Nine Inch Nails and Depeche Mode and Fugazi right along with me. His favorite song as a preschooler was “Personal Jesus”. I was a young mom, and not “mature” enough to buy the notion that I had to stop listening to what I liked. I took a lot of flak for that from my parents, other parents (who were generally older than I) and even his teachers.
(When he was 10, he came up to me and excitedly asked me if I had heard of “this great new band…Nirvana?” I had to explain that they had actually stopped playing the year before he was born, but I hadn’t really cared for them at the time, so that’s why he didn’t know them.)
But I wasn’t alone, just a bit ahead of my time. The same generation that saw no need to put down the video games after college has also kept control of the stereo, and kids now are more likely than not to be listening to and enjoying “regular music” as well as classic nursery rhymes and " Clean up, clean up, everybody, everywhere…" (Which is the best song ever for programming young minds.)
So, for most kids that I know of today, the answer is “both”. Kids listen to kid music AND regular music - if nowhere else, Raffi is still king of the preschool.