A bud of mine rides an Xtracycle based on a modified Trek. Works well but don't put one on your 3.5 lbs Columbus racing steed, they'll destroy it. Find that old 1985 Schwinn High Plains or straight gauge 7000 series GT and modify it. Also be sure to get the tire driven blender option. Seriously. Cruise in style, laughing at the suckers in theirDrew, I think THIS is the company you are looking for. =)
I used to have a bike trailer for my boys when they were young. Like 2 and 8 months...