You’ve got that right...prayers...and more prayers..
I lift them up in prayer as well. This young man probably thought he could pull himself out of the sand and be okay - I know boys frequently overestimate their own strength at that age. Children are children, and they will do some very dangerous things; so many young lives are lost not because they were bad, or stupid, but simply because a careless momentary thought went terribly wrong...
God comfort his family, and help them with their loss.