True, this market is probably the biggest of all, even outselling romance, and yet I do not write for children or pretend to have all the answers regarding this genre. Since this is the case, I have researched the net and have come up with a source to lead you in the right direction. Someone should pay me for all my work. Remember, Steven Walker's Writer's Web showed you the way. The best way to learn how to write for that age group would be to expose yourself to them and listen.
Children afford the greatest insight on what they like best.
Keep in mind that pre-kindergarten age children are generally limited when it comes to their ability to read and you may want to get together with an illustrator. Next, research your market by visiting the local libraries and checking out books that are similiar to what you are proposing to submit. Find out who published these books and contact them. Send a simple letter requesting submission guidelines and then query them with your idea before sending any manuscripts. Often times, publishers prefer to find their own illustrator for children's books.