How exciting!! Congratulations!!
I suggest you first contact your local chapter of the Society of Children’s Book Writers and Illustrators, explore their message board and check out all the resources they have available. Next, find a critique group either in your area or online. Here’s great advice about finding a group. Honest critiques of your manuscript are a necessary step in getting published. Then be prepared to revise and rewrite until it’s right. If you need a fresh read of your picture book manuscript, check out my Picture Book Peek Weeks on my blog. You can sign up to be notified of upcoming peeks via my contact form. Also, see my article “Does Your Picture Book Premise Have Power?” and test your manuscript against my list. When you’re ready to submit, The Children’s Writer’s and Illustrator’s Market will be a valuable reference.