We have used David Adler in the past and he was excellent. He wrote all the Cam Jansen books as well as a ton of other books including many history style books and books on famous Americans for kids. He lives in Long Island and will come to NJ. His fee is also nominal compared to other authors of his caliber. He was the kindest man and his presentation with the kids was really awesome. The children just loved him. He signed all of the kids books and then went to the library and signed all the books of his in the library as well. He literally spent all day at our school.
He has his own web site
http://www.davidaadler.com/ If you email him he will personally email you back. We actually booked his visit with us personally as opposed to us having to book with his publisher. This is better as the publisher will require that you buy his books through them at their price. Since we booked with him personally we were able to go to Barnes & Noble and buy a ton of his books at a discount and then return any books we did not sell.