My girls (age 4 and 1) love and look forwarding to going to Gyminny Kids where they learn the basics of gymnastics. The teachers are great and really good with the kids. While it's fun, they are also there to learn, just like a professional gymnast.
They offer many conveintly scheduled classes for different age groups. The classes are somewhat expensive but they offer various discounts (multi-class, sibling, daytime).
There is a shop that sells gymnastics apparel and other gifts. Parents can view classes from a viewing room upstairs. The waiting area for the gymnasts has a t.v. and some activities for the kids.