The ideal spot will have plenty of nearby parking, lots of open areas, restrooms close by, and some fish. Don't think you have to send each kid home with a mess of fish. Make the fishing fun. There is more to fishing than catching tons of fish. You want to give them a realistic idea of what fishing is, and fishing is not catching.
Tangled lines are easier to deal with in the middle of a field than on the bank.
Keep telling yourself that this is supposed to be a good time. This will reduce the chance of an avalanche of people showing up.