We have six kids, oldest is out of the house in college, next boy is a senior in high school and works for me (homeschooled).  The other son is a freshman in highschool, and his three sisters are in elementary school.

Our rules have always been as follows:

1.  Absolutely no activities that don't involve the rest of the family on Sunday.  
     No sports, no auctions for dad, no shopping for mom.

2.  Each child can play one sport per calendar year.

3.  Everyone eats at least one meal together every day.

4.  No overnight out of town travel for sports.

5.  Everyone home by the 10:00 news.

6.  Everyone goes together on vacation once a year, mom chooses where.

7.  Activities that cause you to miss your chores repeatedly are canceled

8.  The cost of sports/activities are paid by the kid doing it.

9.  When in doubt, the answer is no.