Oftentimes as I'm studying plant families, I wonder what their evolutionary relationship is. The Tree of Life web project compiles the phylogenetic work from biologists around the world. Its user-friendly format makes it easy to see genetic relationships.
http://tolweb.org/tree/phylogeny.html

The Tree of Life includes phylogenies of:
Land Plants
Animals
Anthropods
Terrestrial vertebrates
Fungi
Eukaryotes

It also is an incredible resource for kids! Plenty of biology-related activities to keep your child's mind active with scientific goodness:
The Treehouse for Kids