When my kiddo was little, I pulled him in a trailer. I liked the trailer because it was large and visible, he could have toys and books and juice in there with him, he was covered, and if I tipped the bike over he would stay relatively safe.

It was *wide* though! And I was riding on pretty easy-going streets.

Here in Seattle I've seen a few folks commuting on the busy downtown streets with little side-car style kid carriers. Very narrow and right next to the parent so you can see each other and the total "vehicle" isn't any longer than a regular bike. Not sure how the coupler works, if the bike tips what happens to the side-car, but they look really ideal for maneuvering through city streets.

This looks like what I've been seeing: http://www.bicycletrailers.com/Chariot-SideCarrier.pro