-- Last Updated: Jan-19-13 10:44 PM EST --
Lee makes a good point - you may be better served by building a strip canoe big enough for the three of you. I have no experience with a canoe that big, but Newfound offers some nice designs, cedar strip kits, etc. and are not too far from you in NH.
Guillemot Kayaks offers a high-capacity double strip canoe that would probably suit your situation:
It won't be long before those boys want their own boats - maybe consider fuselage-style kayaks for them when that happens, they're light, inexpensive, quick to build: