I forgot to mention the real value to taking your children on Bay Area public transit: They'll learn how to fight.
There was this scuffle on a Chinatown Muni bus last year.
And then more recently, a fight broke out on an AC Transit bus in the East Bay. The winner of the fight is now being referred to as "Epic Beard Man." Someone even did a "Mortal Kombat" mashup of the video.
Maybe the real lesson is to start recording any disagreement early, so you can get a nice YouTube clip out of the bargain.