I have been both to My Gym and Gymboree and they both offer awesome tumbling classes for kids. However, the cost about $74-84 a month. We discovered that our city parks and recreation department offers classes as well for a little less, but they don't seem to have the vast equipment the gyms do. So, you may want to check your city's parks and recreation department to see what they offer.
As for swimming lessons I absolutely loved Waterworks in Irvine. They teach the children in a very warm, enclosed, salt water pool and the instructors are just amazing. However, they do cost a pretty penny. We were able to get some great quotes from Swim Venture, which has a variety of locations, but honestly I have not heard as many great comments on their program for little ones. Another option is to also check your city parks and recreation department for swim classes. They would be far more reasonable.