Don't use special fonts or scripted fonts unless you have a special reason for doing so. Keep in mind that your audience is just beginning to read and you should use the fonts that are most commonly seen by them.
Children trying to identify letter when learning - need to see consistency. With only the examples of "A" below - look at how many different characteristics that one letter has in these seven different fonts. A child learning to read and write could easily become confused.
Aa* Aa Aa Aa Aa Aa Aa
Gg* Gg Gg Gg Gg Gg Gg
*AvantGarde Bk BT
Content
Word choice is critical to the sale of good children's book.
If you are using words that are not age appropriate - too complicated for your reader, regardless how good the content is, you might have already lost your audience. Test read at the schools or libraries in your area and ask them to raise their hands if they hear a word that they don't understand. Don't change your word choice based on one or two children not knowing the word, but if you see the same response consistently, then you are getting a clear message that the word choice needs to be made more appropriate for your audience.
Accountability
Psychologists say that the major part of anyone's personality is permanently shaped by the time they are eight years old. This means that the author who writes for children needs to be exceptionally vigilant when expressing their core concepts and ideas. More than any other author-set, they are shaping future adults. Fortunately, most of these authors have a very specific and usually positive message, and they should be commended for expressing it in a forum that really matters. This is the most important audience anyone can write for - remember that!
