Firm echo on the chin chaffing problem with PFDs for the little ones. Before our kids graduated to better fitting PFDs we sewed soft fleece patches on the upper part of the front of their PFDs to prevent the dreaded chin chaff. A sarong or two is nice to have to cover them from bugs, sun, chilly breeze etc. Snacks, snacks, snacks. Bring more than you think you need, especially if there are other kids on the trip, as you will be sharing. We have a sand toy bag (others use a bucket with gamma lid) that is rigged on top so it can be immediately deployed at lunch stops and when you hit camp. Contents of sand toy bag: a couple of small garden trowels, a couple of small buckets, small balls (golf ball or little rubber balls) for sand trail luges, a few cars and trucks, a few little squirt guns, some toy boats and a few large fish tank nets. It is also nice to have a bunch of books at the ready that you can read to them for distraction on long days or to help facilitate napping.
As adults, it is easy for us to balance a slippery plate on our legs to eat, not so much with the little ones. They will drop their meal on the ground faster than you can say.... and then the tears are flowing. We used their little compartment lunch boxes to serve their meals to them, or we just fed them from our plate.
And they must wear their PFDs anytime they are near the waters edge. No matter what.