Even picture books that don't rhyme should have rhythm. The sentence length, phrasing, and words should be carefully selected to optimize that rhythm. It sounds like that's what you're doing.
If you're talking about picture books that are in an "official" non-rhyming poetic form, I've seen a few picture books written in haiku.
I would say that if your "line breaks" make sense for the rhythm of your manuscript, that's how you should write it up and submit it. You can briefly explain it in your cover letter.
I'd love to see more non-rhyming rhythmic picture books.