Small publishers are a solid idea; the “big” houses don’t publish every book out there, after all. Smaller houses often know how to target niche markets well, and they can be more willing to take on books that don’t scream “bestseller” from the git-go. The Literary Marketplace (LMP) is a great directory of American (and Canadian) publishers of all sizes, available online and in book form. But since you’re writing MGs, Children’s Writer’s & Illustrator’s Market might be a better place to start, as it focuses on the children’s book industry. In both resources you’ll get publisher contact information, specific editors’ names, and each house’s topic/genre preferences. Do research each of your potential publishers online, as the definition of “small publishers” is morphing daily with advances in digital publishing and online marketing capabilities. You want to find the right level of “small” for you. At your phase of submission, I recommend you aim for long-established houses, with a solid backlist and proven professionalism. Don’t be afraid to stand in your local bookstore for a few hours at a time, opening up books similar to yours and checking the copyright page for its publisher. I think you’ll be surprised by how many smaller houses are getting books into stores.