It ain't easy to talk about the form and meter of this poem, but here goes. The most straightforward thing to notice is that Cummings' constructs the poem in nine quatrains, or nine groups of four lines each. There isn't any regular meter to the poem, but if you read the thing aloud, you'll notice that Cummings sometimes slips into a meter that sounds like a children's nursery rhyme. Just check out the emphasis in the first line:
anyone lived in a pretty howtown
You can almost feel the baby bouncing on your knee as you read this line, but this steady meter doesn't continue on in the poem. Instead, Cummings' drops into a more meditative and freer rhythm, which helps convey what the poem as a whole is doing. Cummings is basically telling the story of a typical American suburb as though it were a nursery rhyme. But his overall point about human life being killed by conformity and endlessly destroyed by the cycle of nature is something more adult in theme.
Every now and then, Cummings will make two lines rhyme, as with lines 1 and 2 of the poem. But he never settles into a pattern because that might give us a sense of comfort that he doesn't want us to have. He wants to unsettle us and to make us think about the stuff we take for granted, and it's easier to do that when you use a rhythm and meter that keeps people off-guard.