Last time around, Anna (who, by the way, has re-designed her blog again, so go and take a look) posted this one in the comments:
12. You know you're a parent when (brace yourself, this is gross) you get projectile vomited on...and you clean up the kid first!
So here's #13:
13. You have ever participated in a game involving three players, ten plastic bowling pins, a soccer ball and a hockey puck.
Oh, and no rules that anyone can figure out.