Judging from the campsite video ,they weren't swimming off a beach. Park lakes are known for their drop off and shelves ( speaking as a fisherman ) .You can be in chest deep water ,move a few metres and be over your head and then some. Figure that's what happened to the kid. Way too remote a trip for kids such as these. 
His father on tv said he couldn't swim and didn't take any swim test . School board rep said all the kids did and passed. Time to call the lawyers !