First off it has nothing to do with sand or heat and everything to do with water, it does not occur during submersion in the water but 24 hours after swimming or even bathing. It can happen If the child inhales water through his or her nose or mouth and it causes a spasm in the air way causing it to close up. And again this is rare and there is only 1 to 2 percent of drowning incidents but I feel like this is still good information to know.
Now you might be freaking out cause I know I was when I heard this was a real thing. Now I watch my kids extra careful after swimming. The good thing about it is that it don't just happen out of nowhere there are symptoms and sign's to look for those are:
coughing
chest pain
irritability
vomiting
trouble breathing
sleepiness or drop in energy level
There are a few ways to prevent this:
-Give them swimming lessons.
-Keep an eye on them of course.
-Wear safety flotation devices.
So really the most important thing is to just keep an eye on your children while swimming or in water and check for any of the signs.