They'll only float if their lungs are fully inflated with air (from your link and my own experience). If they've been choking on water and are now drowned (as opposed to drowning) I would assume that's no longer the case.
One of the ways I have fun in the water is to breathe a good amount of my lungs out, and sit on the bottom as long as I can. Sit, not hold-by-swimming. It's an incredibly effective way of learning how to control your heartrate & panic response to holding your breath, because it's hardly possible without control, and then it's pretty darned easy.
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