What do the green hill and the meadows do in the poem ?

 This AABB rhyme scheme is often used by Blake in Songs of Innocence to evoke this sing-song quality of children's songs, and by extension their innocence and unquestioning joy at life. The “Laughing Song” is truly a song, intended for singing aloud, with a simple rhythm inviting an equally simple melody. Blake himself was known to sing his songs aloud.