-- Last Updated: Feb-20-13 11:36 PM EST --
You've received some good feedback regarding rigging the canoes; I won't add anything to that subject.
However, I would suggest that you have some practice sessions, with all participants, prior to actually getting on the river. Practice the recovery of people, boats, and gear. The time for such practice is NOT the first time those things occur on the river.
When I did river trips with scouts, every participant was trained in first aid, CPR, Basic Water Safety, and Intro to Canoeing.
Adults who accompanied the troop on those trips received the same training.
NO training; NO GO!
On the river the lead, center, and drag canoes were always manned by at least one adult, and all 3 of those boats had rescue gear available.
The scouts got a lot of boat recovery practice; assisting other paddlers who had "no" training.
The scouts were not allowed to "play games" while paddling; that was for break time. Not staying on schedule resulted in no breaks. I took most of the responsibility away from the adults; gave it to the scouts. They dealt with it just fine, after they learned the concept of receiving "natural consequences" for unacceptable/unsafe/childish behavior.
In many cases, the scouts handled things better than some parents who participated in the outings.
Scouts were broken down into food groups, and were responsible for their own meal cooking/cleanup.
Each food group had their own area when camping.
Food prep for the outings was done by the scouts.
Scouts inspected all campsites every morning for cleanliness/no gear left/fires out, before departure.
Scouts inspected all canoes for proper rigging every day before putting on the river.
Scouts assured that canoes maintained distance between each other while on the river.
Any canoe capsizing resulted in all canoes stopping & preparing to assist, if necessary.
Made my trip & theirs a lot less hassle, and a lot more fun, in my opinion.
I used the same methods on backpacking, caving, rockclimbing/rappeling, and Philmont trips.
Kids don't learn much (except irresponsiblity) when adults make all the decisions, do all the work & accept all the responsibilities.