: I would love to get a quality design that is
: stable in the water

I think you need to 'nail down' your requirements more precisely.
Are you looking for a 'rec kayak' type of boat with a big open cockpit, or a sprayskirt-type sea kayak ? What range of paddler weights will this kayak suit?

(I'm not much of a paddler, but 'stable in the water' and 'quality design' don't necessarily go together for me.)

If you want to teach lessons with the building, I think a wood boat (strip or S&G) would be a better bet. Building a straight glass boat from a mold sure doesn't appeal to me. And, it is tough to get a good light composite boat without vacuum bagging and the right layup schedule. It won't be much fun for the kids if the boats are heavy.

Wood building with glass/epoxy over would be cleaner and take longer as well - you won't teach a lot of life lessons popping a boat out of a mold after a few hours work, IMO. Any kid can drill panels and wire together a S&G hull, or staple strips on a mold (if you have a design that isn't too twisty to strip easily). And they have the potential for a lot of "patience, grasshopper, patience" lessons.....
;-)