What does the boy's drowning symbolize for elizabeth?

The boys drowning in the Harlem River contribute to the symbolism of fear and danger  in a community with an weird mixture of good and bad people.

In the Rockpile by James Baldwin, the neighborhood is full of perils where mothers try to keep her sons from the violence that  surrounds them nearby as well as many other hazards.

Explanation:

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in our power to make a world happy - to teach mankind the art of being so - to a character hitherto unknown - and to have, as it were, a new creation intrusted to our hands, are honors that command reflection, and can neither be too highly estimated,