It's been my experience that reputable children book publishers all provide these three crucial children's book publishing offerings:
1. Illustration services via professional childrens book illustrators. I've blogged before on the importance of high quality children's book illustrations and my opinion hasn't changed: Your children's book must have professional high quality illustrations if you want to have any chance in the highly competitive children's book market.
2. Reputable childrens book publishers also offer different book format options. Essentially you should be able to choose hardcover, softcover and/or ebook formats. My internal sales figures show that print is still dominant in the children's book market, so make sure not to skip print. My advice is usually to publish childrens books in multiple book formats if possible.
3. If you're looking to publish a childrens book you should also be sure to align yourself with a children's book publisher that prints in full-color. Believe it or not, I've seen publishers only offer black and white printing (for the interior). That sort of publisher would obviously not be a good fit for your children's book containing beautiful, colorful illustrations.