My local elementary school fourth graders celebrate Arbor Day by entertaining the community garden club with a variety show all about trees followed by the ceremonial tree planting in memory of a garden club member. Do any other communities do the same? It's a wonderful tradition.
If you're interested in creating some Arbor Day festivities, maybe as a prelude to Earth Day, I've found some wonderful resources. First, get everyone in the spirit by playing The Lorax's Save the Trees Game (http://www.seussville.com//games/lorax/). Of course, as a librarian, I recommend reading Dr. Seuss's wonderful story as well.
http://www.arborday.org/kids/). You'll find online activities, printables, and contests to share with kids of all ages. From the educators' link, you can access Arbor Day video and other resources. This site alone could provide all the Arbor Day activities and lesson plan ideas you could want.
What Tree Is It? will identify trees by leaf, fruit or name. A link gives background information about the anatomy of leaves or fruit. Links also redirect visitors to the Ohio Department of Natural Resource's (ODNR) Division of Forestry website that is rich in information about trees in Ohio and includes education resources as well as Ohio Big Trees, another subsite of the ODNR. Want to know how to measure a tree? You can find that out at Ohio Big Trees. As an Ohioan, I have access to this site; I hope you do as well. If not, let me know and I'll see what other sites I can find in other states; or check your state's Department of Natural Resources or Forestry Department for information they may offer.
Now, get out there and hug, or plant, a tree! :)