Sports for Kids

Do your kids play sports?  Do you have a rule for how many sports/activities they should play each year? 

My kids do a number of sports - soccer, baseball, tumbling, dance.  I find myself debating over the need to start eliminating activities, but how do I help my kids decide which ones have to go?  I would rather my kids be really great at one or two things then average at 5 things.
 

What do you think?  How do you have a good balance?  Am I overthinking this too much and is there a magical age where you have to start worrying about focusing on one sport?