Every agent sees too many (way, way too many) picture book submissions in rhyme. Nearly always it’s poorly done. Forced, dated or generally drecky rhyme results in souring the already skeptical reviewer on the project. Particularly painful is writing with end rhyme of every line. It feels like a hammer pounding away. Usually. Few people can get away with it. George Shannon is one, in his glorious HANDS SAY LOVE (Little, Brown). Part of his secret lies in varying the rhythm. But he has other secrets you might detect upon close reading.
If you haven’t tried writing your story without rhyme, this is something you must do. Perhaps you’ll conclude it works better in rhyme, but push yourself (and your characters and story) to be sure.
Rhyme works best in combination with other language devices. Elizabeth Verdick’s SMALL WALT (Paula Wiseman Books/Simon & Schuster Books for Young Readers) is a great example. Rhyme appears only for special emphasis and effect: a) when Small Walt (who is a snow plow) thinks, and b) in six lines that most strongly convey the drama of the story. Much of the rest of the language energy comes from deliciously snow-plowish sound effects Walt makes, and perfectly chosen words to convey the snowy night struggle.
My suggestion? Create a great story. Find the best language to house that story. (They’ll probably evolve together). Explore not only rhyme but parallelism, alliteration, rhythm and repetition. Find out what’s natural and what enhances your characters and brings the story to life. Aim at a great read aloud, with words that are fun to say and refrains a child will anticipate with delight. To get there, have other people read your picture book manuscript aloud to you because you may “hear it” in your head in a way that’s different from what you’ve put on the page. It may lead you to a good revision.
Keep in mind that many editors will simply not consider stories in rhyme. Perhaps they are being narrow-minded but that’s the reality that your agent is facing. Rhyme can be tricky to translate (though HANDS SAY LOVE has been). You may be doing yourself a disservice by pitching a story in rhyme, given these realities. So, if you use it – use it really well.