I saw this, and it got me to wondering if there were any talented engineers/metal-workers on BF.n who would be interested in creating a similar beast as is pictured here:
http://www.flickr.com/photos/indigoclouds/2767797627/in/pool-74538626@N00/
I was looking around online and found some similar but more dangerous versions of this (i.e. one where the front-wheels of the wheelchair are on the ground... could be very dangerous as their small diameter lends to them stopping suddenly for bumps/rocks/etc... One with obviously no front braking....)
If you (or know of someone) who has the skills to come up with a way that I could take my son on my bike trips, or if you know of an existing product that fills the need, I'd be grateful to hear more about it!
My initial thoughts on requirements: