Thanks for the plug, Mike! Actually it's called the "Coos 8." Both of my daughters (2-1/2 and 4-1/2) have one. It's 8 feet long overall and 18 inches wide. The offsets are free. Plans will cost ya! ;) I'm in the process of reworking my website and still need to make a page for that design.
http://clearstreamwood.com/WordPress/portfolio/kayaks/skin-on-frames

For a 5 yo, I'd probably recommend making it a bit longer. Say space the forms out so that it's more like 10 feet long. He'd be fine in the 8 footer (it's rated to 70 pounds) but the 10 footer will give an extra year or two of use before he outgrows it.

If you want build a boat with wood hull, consider "skinning" the frame in luan plywood. The next boat for my 4yo will be built like that hybrid "Elsie" I built a few years back. It'll have a plywood hull with a deck skinned like a SOF.

=D

: Dan Caouette has a design he calls "Coos Bay" that is
: smaller than a Sea Flea, so you won't even have to compromise on
: size.