Kids that age have been walking around independently since the dawn of time. Kids that young can know how to swim. Kids that young can be taught basic boundaries and responsibility.

Some searching suggests the drowning death rate for children globally under 5 is 7 per 100,000 per year, lower in the US. Yes, it's the second leading cause of death of kids, but it's not a high risk. A child has just a 0.035% chance of dying by drowning before their 5th birthday.

It's always tempting to say, "but no risk is too low!" But that's idiotic reasoning. Every method of increasing safety also inevitably decreases freedom, independence, and the development of proper self-sufficiency. Every choice to mitigate risk has to be balanced against the long-term risks of preventing kids from growing up into full and independent adults. Lack of freedom stunts emotional and social development and the growth of street smarts. These imprisoned children are then cast out into the world after high school completely unprepared to actually live as independent adults. And they crash and burn.

Even if all you care about is safety, you have to balance multiple life risks. For example, we've taken away most of the freedom from our children. They have very little ability to move about in the world on their own. This means they don't really start developing independent life skills until they're in their late teens or even til they graduate high school. And they're going to have to leave the nest eventually. And the less they're prepared for the real world when they're minors, the more they have to figure out when they're out all alone and without close parental support. You can prevent some childhood deaths by taking away children's freedom, but in turn you increase the chances of them dying early deaths of despair in their twenties. The kid that never has a chance to grow up suddenly has to do all their growing up all at once when they're a legal adult. This leaves them unprepared and at high risk for a complete failure to launch, drug addiction, and overdose. Kids who are never allowed to grow up become adults who can't cope with the world and end up dying from heroin overdoses.