I am not yet a mother, but I grew up in LA and did attend Beverly Hills YMCA Day Camp. Although it is no longer there, the Westside Family YMCA should.
Westside Family Ymca
###-###-#### www.ymca.com
11311 La Grange Ave, Los Angeles, CA 90025
I had a great time every year!
LA Dept of Parks and Rec also offers programs similar:
http://www.laparks.org/dos/camps/camps.htm
Here is a link for the bowl-- I don't think it's music classes, actual hands on, but you may want to check it out:
http://www.hollywoodbowl.com/tickets/summersounds.cfm
My friend has a great studio on Pico near Fairfax: "Creative Seeds"
http://growcreativeseeds.com/
she usually offers a great program in the summer including dance, music, art, theater, yoga, etc. I'm sure you can send her an email and she'd get back to you right away. The vibe is very warm, supportive and welcoming. I can't wait to get my baby-to-be there!
Hope this helps! Have a great summer.