There is at least home page on the web dedicated to fractals: www.fractals.com
In a simple way, fractals are patterns that self-repeat but it would be more fun to visit the page than to hear it from me.
There is a book called Fractals for the Classroom by Peitgen, Jurgens, and Saupe and published by Springer-Verlag. It is a great book and has some supplemental booklets but I think it is above the middle school level.
Scott Smith Academic Dean The Lovett School Atlanta, GA