maggie and milly and molly and may went down to the beach(to play one day) (1-2)
From the beginning, we hear the speaker's young and playful voice listing a bunch of names that sound alike and rhyme. These girls are the epitome of youth and fun, especially since their main objective is to play. Little do they know they'll soon stumble upon some of our most coveted universal truths (of course, knowing that would defeat the whole purpose of fun).
milly befriended a stranded star whose rays five languid fingers were; (5-6)
It's a lot easier to identify with nature directly when we're young and our imaginations are still healthy and intact. Older folks tend to forget all about the importance of imagination and how simply looking at a starfish might remind us of ourselves in some way. This starfish has fingers like a person, and the speaker's use of personification seems to make milly look a little less lonely.
and molly was chased by a horrible thing which raced sideways while blowing bubbles:and (7-8)
There are boogie monsters at every turn when we're kids and more often than not we're not quite sure what to make of them. The same is true here as molly is chased by a weird-looking creature that's blowing bubbles at her. The speaker doesn't call it a crab because molly herself probably has no idea what to call it either. Nature's frightening creatures also seem to symbolize the kinds of scary things we all encounter in our adult lives that we usually handle in the same way molly does: by running away.