The great thing about school presentations is that authors are often paid a speaking fee in addition to being able to sell their books.
See these two articles for tips about promoting in schools:
How to Market Children's Books in Schools by Melissa Williams
Making School Assemblies Fun by Sheri Bell Rehwoldt
Virtual Author Visits
You aren't limited to schools and libraries in your area, because you can do presentations to kids around the world through the magic of Skype. And if your day job prevents you from visiting local schools and libraries, you can visit kids in other time zones through Skype. In this podcast, Margot Finke shares her experience with doing Skype visits to schools.
More Resources for Children's Book Authors
Author training program: How to Sell More Children's Books