S.M.
The Boca Ballet Theatre (http://www.bocaballet.org) is very well regarded, and your kids will not only learn from great dancers, but will be exposed to MAGNIFICANT ones. (Dan and Jane pull in principals for their performances from some of the most outstanding companies in the country).
Depending upon what you want to do, both Twisters and Star Gym are excellent facilities that allow your kids to either have fun and learn discipline, poise and coordination, or to take the Amateur Athletic Route and compete if they have Olympic aspirations :)
Star Gym is on W Rogers Circle off of Clint Moore Rd, between Congress and Military; Twisters is in one of the industrial parks on Boca Raton Blvd, between 20th and Spanish River.
There are lots of Tennis facilities around, but if you live within city limits, the lessons at the Community Center (City Hall; Palmetto and Boca Raton Blvd seemed reasonable, our boys aren't quite ready for tennis yet.)
-Scott (S.'s Hubby)