I believe the legal term for that is “depraved indifference.”
I'm not a lawyer, but this link suggests that depraved indifference only applies to reckless conduct that the guilty party engages in - such as driving while drunk, or firing weapons wildly.
There are three parts of the test for this offense. One requires the defendant to cause the death. In this case the defendant hasn't done so; the children drowned. Another requires the defendant to engage in reckless conduct. In this case the defendant did nothing. The third part requires that the court finds that the defendant acted with depraved indifference to human life. In this case this is probably true. But all three parts must be true to convict.
Being an a-hole is not a crime. Leaving someone without help so that later on that person dies is not a crime either - humans generally cannot see the future. One could think of a contrived case where someone is in imminent danger and you can help. For example, a robber is about to stab a child and you can shoot the robber in time. There is no law that would require you to do that. I think one of the reasons for that is that the law wouldn't be enforceable. A passerby "will not notice" the robbery three feet away; a homeowner "will not hear" the knock on the door if these actions can expose them to a charge of murder. In case of assault that is already likely today: a pimp pulls a gun on his worker; you protect the prostitute and wound the pimp; then they both say that they were standing still and you are just one of them raysis, like GZ, walking around and looking for a minority person to shoot.
But that's just general thinking in that direction. I do not believe the man actually denied entry to a woman in distress. He may have rejected the idea of swimming in cold water, at night, trying to find someone - even a platoon of Olympic swimmers in dry suits wouldn't find anyone in rushing black water. As other posters said, there are several versions of the story, and there is no need to rush to judgement. I'm sure the death of two people will be properly investigated by professionals. At this very moment the guiltiest person in sight is the mother who failed to take her children to a safe place ahead of time. Everything else just failed to salvage a barely survivable situation.