Update March 8th, 2023: Website not working. Consider defunct.
ThunderStone Books’ motto is global education for young minds. They focus on publishing children’s books with an educational aspect. The attention is particularly on books exploring a new language/culture in a fictional setting. Their area of primary focus is Mandarin Chinese (language, culture, setting and/or mythology). But they are open to other languages and other subjects, including science and math. They also consider fiction without a strong education focus, but that is not their forte.
They publish picture books and chapter books. ThunderStone Books appears not to have a distributor. Their website seems aimed at parents and teachers, which is a good sign. The cover art quality varies wildly.
ThunderStone Books has only published seven books so far, which is not much of a track record, but it makes it easy to get a feel for what they publish. They are a very small company run by a husband and wife team and you can learn more about that here.
They accept all submissions through email. If your manuscript is less than 50 pages in length they ask that you submit it all. If your manuscript is more than 50 pages in length they prefer that you only submit a query letter.
They try to respond to all submissions quickly but it can take up to six months. If they are taking longer than six months to respond to your submission, please feel encouraged to query about the status of that submission.
You can visit their website and review their full manuscript submission guidelines here.