As a parent I've always thought it will be best for me to expire before my kids, that should be a rule. It is sad the child is gone; I cannot imagine what the parents are going through. How very saddening.
I'll likely never know, but first thought after the sadness was I bet the kid wasn't much of a swimmer, possibly due to our economy and a lack of places to learn self rescue, floating, treading water, etc. Remember when there were Red Cross classes to learn swimming, first aid and C.P.R.? Not much of that being offered any longer; not many open swimming pools.
I don't know that I've ever seen a bank fisherman with a PFD. However, if you are not a confident swimmer or facing very cold water as troutdude mentioned a PFD would be a nice piece of insurance. For certain if you use waders you need a tight fitting 1.5-2 inch wader belt. If they happen to be neoprene waders so much the better, they have tiny air pockets and add flotation.
Be safe out there.