My life was once full of interactions with children. Now that I work in an office instead of at a pool, I see children very sporadically. My off hours are spent in comedy clubs and bars, where children are not allowed, because they would get too depressed about growing up.

The children I do encounter fall into two categories: Babies, and children in large groups. The babies are pretty harmless, and, let's be honest, none too bright.

Children are a different story. It may be that city children are tougher, or it may be that most adults see them only sporadically, but whatever the reason, groups of children are horribly intimidating. They're far more powerful in groups than they would be individually, their numbers and the urban environment giving them courage and defiance not seen in suburban children. Like wild animals, they are more feared than understood, and people don't like to make eye contact.

I was on MUNI on Tuesday, and a large group of fifth-graders entered, en route to a play. Instantly, the mood of the train changed. Hipsters clutched their messenger bags closer. Adults looked at one one another and nodded, as if to say, I've got your back if anything happens.

One Asian kid pawed at my book and demanded, "What are you reading?"

I stammered, "Um, it's called, How Soccer Explains the World." I braced myself for a followup question, but he was distracted by a tiny scowling white girl lurching into the back of my seat. When the fifth-graders exited at Civic Center, you could hear the entire train exhale in relief.

Perhaps in San Francisco, we fear the unknown, these pint-sized invaders of our fair city. Or perhaps I am unable to deal with children when I'm not allowed to pick them up and throw them into swimming pools. All I know is that San Francisco children make me nervous, MUNI is for grown-ups, and I don't even want to think about packs of teenagers or else I'm going to break out in a cold sweat. Parents, keep that stuff in Cow Hollow where it belongs.