A group of people stand together and look at the water where a child died, not long ago. That is all the poem tells us outright, and it says it plainly, almost like a report. The speaker is one of the "we," so they are not watching from a distance but are part of the gathering, sharing the same stunned attention.
Then the poem turns to the dead boy's little sister, "calling." The word is left hanging, with no punctuation and no answer. We don't know what she calls or whom she calls for, and the poem doesn't say. Judging by the way it stops, she may be calling for her brother, and the silence that follows is the cruelest part.
The mood is hushed and heavy. The short lines and the white space around them feel like held breath. The speaker doesn't explain their grief, and that restraint makes the moment hurt more.