There are many good summer day camps in St. Louis area. STLToday recently has a good piece on this topic.
Personally my old daughter has been to the JCC Day Camp, and Andrews Academy. We like both, with a bit preference over Andrews: for its after care, and overall quality. Note cost-wise, Andrews is a bit more expensive than the J (about $1,300 per month vs $220 a week for the J). We also thought about the Arts Camp at COCA too but the pickup and dropoff is a bit challenge (due to half day schedule). Note they do have 2 locations: the U city campus and the Whitefield school at Ladue/Mason. My daughter was very much interested in the arts, that’s why we signed up the art camp at the J when she was 5 (incoming kindergartener). This summer we are thinking again sign her up at Andrews (4 weeks Science camp and 4 weeks Outdoor camp). Both the J and Andrews do swimming once a day.
For the little ones, the summer camp at Hope Montessori (Mason road, Creve Coeur) is very good. We are thinking about signing up younger daughter this summer.
Other camps I heard about: the mad science summer camp, and the Lego (Robotics) camp at Maryville U. Both are half day, so it’s a bit challenge if both parents work full time and in office.
Btw, I wrote about the summer camp about 3 years ago.
Last but not least, found a summer camp search website here.