We also do generally do one active, one musical activity for the most part for DS7, and DD3 (she's only in preschool 3 mornings a week) now too. We are hoping to start DD3 on an instrument in the fall - suzuki violin if she has her way. She's doing kinder musik type program now. DS7 has been taking piano for almost 2 years and started about 7 months before kindergarten. Which worked out really well for him.
I also kind of feel like the free time is GREAT for the kids in terms of creativity and inventiveness. When they're left to their own devices for a couple hours at a time, it's amazing the things they do and come up with. I feel like they have plenty of time to try everything. Both of them would ask to book their schedules solid, but I really feel like we all need that down time.
