There is a class at Byer's Gym from 0-3 year olds. It is parent participation, so be ready to kick off your shoes too. I put my 2 year old twins in it last summer (they are 3 years old now). It costs approximately $50/month for each child. There is also a class (at Byers) through the CSD (http://www.yourcsd.com)
Originally when we signed the twins up for the Byer's class we were on the waiting list for a couple months. It's a popular class! But we also had to wait for two available spots.
There are a couple other options in Elk Grove for tumblers. Funtastic is a great place to let your child let loose. I think it's about $8 per admission, but if you buy tickets in groups (like a 10 pack) it works out to $6.50 per session instead. Another option is Gymboree. I found Gymboree to be slightly more expensive than Byers, but I think the class was longer by about 10 minutes too.