Earlier this year, I had my math differentiation group do some work fractals. I found some excellent resources online just by Googling “fractals for kids”. But by far, the best source I found The Fractal Foundation that has many fractivities for kids, including fractal trees, Sierpinski triangle to name but two.
I wish I had this book to introduce the concept to my group:
Mysterious Patterns: Finding Fractals in Nature by Sarah C. Campbell has fairly simple text, but it explains the mathematical concept of fractals beautifully. Photos from everyday items such as broccoli support the text. (This might be the only really good use for broccoli!)
Back matter provides an activity and more background information.
My 4th graders really enjoyed learning about fractals and felt quite brilliant. We even made a bulletin board of Sierpinski triangles to show off their brilliance and explain fractals to the rest of the school.