I thought I'd come back with a status update. My little guy just turned 3 and I bought a standard Adam's Trail-A-Bike off of Criagslist.
He only has a 12 inch inseam so I cut off .5" off the bottom of the seatpost so the seat could be lowered to the bar. His legs were still about 1.5" short so to test it out I duct taped wood blocks with old D-cell batteries on the bottom as a counter weight.
I' don't know if I'll come up with a better solution or just wait for his legs to grow.
We went on a few rides this weekend and he didn't have any problems or fear staying on. By the end of the weekend I was pretty much going the same speeds as with the InStep trailer. He doesn't really pedal, but I'm sure he'll figure it out on his own soon enough.
Here's the pictures. (After seeing these pictures I corrected the handlebars so he leans forward a little bit!)
