Question

The author repeats the "b" sound in words like "birches," "bend," "boy's," and "been," which makes the lines sound musical and bouncy. This bouncing rhythm matches the image of trees swinging back and forth, so you can almost hear the motion. The repeated "b" also links the boy and the trees together, showing how the boy's play makes the birches bend. But the same "b" in "But swinging doesn't bend them down to stay" reminds us the bending is only temporary.
Answer in a 7th graders words

Answer 1

The poet uses the "b" sound a lot in words like "birches," "bend," "boy's," and "been." That popping "b" sound makes the lines feel musical and bouncy, like a little beat you can hear. It matches the picture of the trees swinging back and forth, so you can almost hear them moving. Using the same "b" sound in the line "But swinging doesn't bend them down to stay" also reminds us the bending is only for a short time — the trees spring back. The repeated "b" sound ties the boy and the trees together, showing his swinging is what makes them bend.