Hyde Park for lonely kids

I care for my two boys, age two-and-a-half and four-and-a-half, in the afternoons here in Hyde Park. Recently. In a parenting listserv a mom new to Hyde Park asked me where to meet up with other children because her girls stay with her on the weekends and have no friends.
Here's what I told her is available for kids in Chicago's Hyde Park neighborhood this summer:
Washington Park Pool is completely free.
As for beaches, I like the one behind/next to the Planetarium, 57th street & 63rd street with friends. 63rd Street has a great fountain kids can play in. And on Sunday late afternoons, there's a very earthy & impressive drum circle. Behind the South Shore Cultural Center is a secluded (sometimes brackish) cove -- makes you feel like you're not in Chicago, although you can see it from a distance.
Bixler is the most popular park to hook up with other parents.
There is a wonderful Saturday youth ceramics class for kids 6 & up at the Hyde Park Art Center. You can enter mid-semester too.
Alternatively, joining the gardening at Kenwood Park, Behind the HP Neighborhood Club or at the Community Garden on the other side of the Midway around Dorchester, could be a great way to meet people.