Though we can't be exactly sure where this poem is set, the references to teachers, books, nature, and the childish actions seen in the parentheses make the poem seem like it's set at a playground where children are enjoying their recess. It's likely that this playground is just in our speaker's head, but, nonetheless, the poem has a childish glee.
More important than the physical place where this poem is set, though, is the type of world this place is. We know from the first line of the poem that this piece is going to describe a world in which "everything happens that can't be done." In other words, nothing is impossible in this world, so when we read we should drop any skepticism that we've picked up from years of living in a world with limits.
In this poem, love can be brighter than the sun, the world can be a leaf, far can be near, anything can be everything, and even "everyanything." Everything is happening, all at once, and it couldn't be more wonderful.