I'm going to agree with the posters for Peterson Park. It's a gymnastic center complete with springboard floors, balance beams, rings, etc. My son has gone for about 8 straight sessions and has loved it. We started him about 20-21 months. There are 18-36 months classes. I don't remember if there were any under 18 months, but the next session starts in the fall (we're in the summer one thru mid-August). Classes are an hour and they have them at all times of day (we did an evening class last spring so my husband could join us - 6:30pm - so it's good with work schedules, too). The teachers have all been excellent!
They fill up fast with registration, but it's well worth the time online (or waiting in line if you do walk in registration). Have fun!