OK, given these criteria, I 'd look at some of the rivers in Maine;
the Kennebec or the Penobscot perhaps. You can get enough length to
give you a multi day trip on water that will be manageable. There are
several outfitters up there who will rent canoes.
Don't let your eyes be bigger than your tummy in the whitewater area.
A multi day trip is not a good place to have a busted boat or a lot
of lost gear or an injured person. If you want to spend time with
whitewater then consider actually going somewhere and doing whitewater
day trips. Take a look at the Nantahala Outdoor Center. Maybe you
want to think about going there and actually learning how to paddle
kayaks or whitewater canoes in whitewater. I bet if you have a group
they would discuss setting up an instruction class for just your
group. There is good camping and you would learn a whole lot about
paddling. It would be very worthwhile to do it so young because even
if you did not decide to become whiteater paddlers, the skill would be
very transferable to future wilderness trips. Plus, you will have a
very good time
Good luck!! Chris Kelly