This is a big problem out there in the publishing world. In all honesty there are way more books, writers, and aspiring writers out there than the industry is able to publish. It has to do with the costs of going through the publishing process, and getting a book printed. There is lots of risk, so a lot of really interesting books get rejected because they pose too high a risk point from the publishers perspective.
Do not take rejection personally, it is just the nature of the industry. There was a neat video clip circling around on the BBC a year or so ago about a mother in the UK who had written and illustrated a number of children's books, and she refused to even try submitting them to a publisher. Her family, friends, and even some people in the industry told her she should try to get published. The reason she wouldn't: she would be heart broken and devastated if her books were rejected.
I myself am big on disrupting this system of mass rejection of content based on risk mitigation. That's why I work for a disruptive publishing company. So take heart, and do not give up on making your books because you are facing a wall of risk mitigation. When in doubt, get creative, and find other ways of getting your book into the hands of kids so you can be read.