The meter and rhyme scheme are irregular in "Goblin Market." The poem generally follows an ABAB rhyme scheme, but not always. In fact, sometimes there's a long gap between a word and its rhyme, and sometimes there are many lines in a row with the same rhyming syllable at the end (like lines 134-136).
Why does it change so often? Why are some lines so much longer than others? What's the effect of reading several lines in a row that rhyme, while earlier bits were in a different pattern? These are all good questions to think about as you read the poem, because the answers will be different for different readers.