I let the grandkids do as much as they want. I try very hard to find ways to pay for their classes like working for the people who own the studio or cleaning one of the board members houses. It is the only way we can afford for them to do anything.
We do gymnastics, tumbling, show team, hip hop, tap/ballet combo, and a kinder gym class that is the first stage for little ones. The younger one also does soccer and T-Ball. We do BMX with the older girl, the younger boy still uses training wheels so he can't ride the bikes for BMX yet. Once he is off training wheels he will use her old BMX bike though.
The girl wants to take piano and twirling and voice and soccer and softball and....you get the idea.
She did tennis this past summer and loved it too. I will let her continue that since the coach allowed us to help clean the tennis courts as payment for the lessons. But as for the rest, she can wait until she is just a bit older and maybe pick another activity. I think once she hits next summer she will start fine tuning her choices. I want her to have a lot of experiences to fall back on to see where her interests take her.
The boy has sensory issues and has a hard time staying in things that are too organized. It is certainly easier for us if he doesn't do anything but it will come, I know he will find some things he likes. I would like for him to like football but only if I can find a way to pay $100+ each semester they offer it. I liked playing in band and going to football games in high school but have no idea of the rules of the game, I think it would be a good outlet for him too.