Holly, there's a great book listed on this site that I have and highly recommend. It's called:
Professional Secrets for Photographing Children by Douglas Allen Box. (If you use this link, Cynthia, who runs SOG, gets a small commission from Amazon.)
I like it because it offers a simple, non-technical approach to posing and lighting kids for portrait photography. He uses only a minimum of equipment and often works with just window light or outdoor light. The book includes easy to understand lighting diagrams and some great suggestions as to how to get kids to pose well, (also a very important part of the process!)