That was actually one of the first athletic activities my dd did(started when she was 3), but she only did it a few years.Nothing competitive, just for fun. I would think that any amount of gymnastics/tumbling/dance would help, and I haven't met a girl yet that didn't enjoy them . Summer break is a good time gives them something to do. Most classes around here are like $35 a month/once a week. There are also places that offer summer camp type classes for cheap.