They'll certainly have fun even if they don't find anything.

Great idea. Teach them how to use the masks, too, plus all the stuff about safe swimming. Get a little class on the beach.........if they come along for the instruction they get a free mask. I was going to say if they come along for instruction bringing a bag of trash which they've gathered from the beach but on second thoughts this may bring you more problems than you'd bargained for..........
