The Arbor Day Foundation has some great information on the history of Arbor Day – including an interactive history book – as well as educational materials that can be used with kids to teach them about trees.
They have a tree identification booklet, an Arbor Day video, online games and activities, and more.
Arbor Day is a great day to pause and appreciate trees. As is custom with Arbor Day – you can also plant one (or more!) that you can then watch grow and mature as you do the same. I love that.