You should never leave children alone in a pool unsupervised.
John is hanging out by his pool with his children who are playing in the water, when the phone rings.
John wants to answer the phone.
John calls out to his neighbor, who is just on the other side of a short fence, to keep an eye on his children while he grabs the phone.
John runs inside to answer the phone.
One of John's children loses her floatie and starts drowning, but the neighbor is able to hop over the fence and save her.
One of John's children loses her floatie and drowns.