Trailercycles (aka tagalongs) - the single-wheel vehicle that attaches to a normal bicycle - have become pretty popular in the past few years.
I looked at a few of these, and we settled on the Burley Piccolo, because:
- It attaches to a rack, and pivots above the rear axle. This means it has less effect on handling than the kind that attach to the seatpost.
- It has gears, so the child can actually help out.
- It has good adjustment in seat and handlebars.
- It has good resale value, because it's from Burley.
We got an extra rack, so we could easily swap between bikes. The downside of the Piccolo is the cost, at more than $300. When we were done with our's, I think we sold it for $175.