The child of a particular age group can only read a maximum number of pages. Therefore, it is very important to take care of the length of the text while publishing a children's book. Now, to get a fair idea of the length, you could consult a few books from the other authors and see their length. For example, an ideal story book has almost 24 pages, four of which are included in the binding. Thus, by making a research you would be able to judge the length that you should render to your children's book.