This instructable will detail how to make a small airplane bicycle trailer. I make these for sale, but am glad if other people try their hand at it. I make a plane, train, tank, taxi and tractor version of these. My son loves this particular trailer (it was my first) and I bet your child will love it as well. It is real simple - just knowing how someone else did it may make your day easier.
For some reason, when I edit this, it will not let me embed video - so here is the link http://www.youtube.com/watch?v=6BdvfXduUso
to my son riding down the driveway in tow.