K.
My daughter's FAVORITE class for the past year and a half or so (she is 29 months) is Music Together. The woman who runs classes on the NW side is Mary Thilleman, and she has classes in Lakeview, Andersonville and Edgebrook. Her Web site is http://merrymusicmakers.net. The class is mixed age, so there are kids from about 4 months to about 4 years. I also have an infant who really seems to enjoy the class! Siblings are free until they turn 8 or 9 months. Good luck!