You should try My Gym, The Little Gym, or a gymnastics place such as SCATS. My son is 4 1/2 and he LOVES his My Gym classes (it is a mixed class from 4-6). They also have classes for older kids. My daughter (7y/o) would love to join a class, but she already has way too much on her plate. I love their philosophy and it is very age appropriate. Besides activities, they also incorporate taking turns, sharing, story time and imagination. The My Gym in Anaheim Hills is nice and clean. We had our son's birthday party there and the staff is very professional and excellent with the kids. We go to the Chino Hills My Gym (and they are just as great)- new facility, awesome staff.
My kids were formerly enrolled in SCATS gymnastics, but my husband and I didn't agree with their philosophy. There seemed to be too much of a push or focus on competition gymnastics. I hear the Little Gym is also a good place. You should also look into city sponsored activities or your local YMCA. They usually have good programs. Hope this advice helps.