I started writing for young adults as a verse novelist. I'd already written poetry sequences and, when the prose version of a story I had knocking around in my head didn't work, I scrapped the five chapters I'd completed and began it again in free verse.
What I discovered in the writing of that first verse novel, A Dangerous Girl, was that the form gave me a lot of freedom. For a start, I could write from the viewpoints of all four of my characters. To do that in a novel would have felt a little clumsy. (Although, of course, it can be done. It's a technique Jodi Picoult uses, just for a start!) I could also directly explore the emotional life of my characters - after all, that's a strength of poetry.
The first challenge was structural - how could I structure the novel so that the reader knew exactly which character was speaking from the look of the poem on the page? I had one character, Leigh, who wanted to be a journalist. So, I decided her poems would all be from the journal she keeps. That meant that the first line of the poem was also the poem's title and it always had 'From Leigh's Journal' as part of that line. Another character, Nick, wrote either prose poems or haiku. Immediately, then, two of my characters were recognisable from the appearance of the poem.
Recording dialogue is another issue in verse novels. I hate to see a page of poetry littered with unnecessary punctuation, so I hated the idea of using a lot of direct speech that required quotation marks. I solved this in my third verse novel, His Name in Fire, by putting all direct speech in italics. However, I believe you need to use less dialogue in this form - it's quite clumsy inserting it into poems. This is a major disadvantage in this form - I love writing dialogue and I love the subtexts you can create.
On the other hand, poetry allows you intensity, lyricism and the opportunity to tell a story in small bites. I think there are certain stories that lend themselves to the verse novel form. To me, younger readers would be a more difficult audience to target than young adults. You need an unforced simplicity for younger readers I find hard to achieve poetically. There's not a lot of difference between writing poetry for young adults and adults - and I prefer writing poetry for that age group.
If you're interested in reading some verse novels I heartily recommend Sharon Creech, Love that Dog, Karen Hesse, Out of the Dust and Aleutian Sparrow, anything by Steve Herrick and Star Jumps by Lorraine Marwood.
If you're interested in verse novels for adults, here's a great list to get you started!