"Nurse's Song" is filled with sonic devices that lend its language with playful music. One of these devices is alliteration, which appears in every stanza and helps convey the children's excitement as they play on the green.
Listen to the /h/ sounds of line 2, for example:
And laughing is heard on the hill,
There's also "heard" in line 1 (also an example of diacope, given that the same word appears in line 2) and "heart" in line 3. The /h/ sound requires an exhalation of air, and this alliteration thus lends the stanza a certain breathlessness. This makes sense, giving the children are running around outside.
The next stanza features alliteration via the shared /d/ sounds of "down" and "dews," the heaviness of which perhaps subtly evokes the coming of the night.
The most striking alliteration, however, is the triple-whammy of /l/ sounds in line 15, which captures the children's reaction when they find out they're allowed to play a little longer:
The little ones leaped & shouted and laugh'd
These /l/ sounds are playful and sprightly, as though the poem, like the children, suddenly has an extra spring in its step. Notice, too, how this alliteration chimes pleasantly with the consonance of "all the hills," ending the poem on a smooth, musical note.