Hi Sean,
One of my fondest memories was making music with my kids and their classmates in their school, and I would encourage you to go for it! Kids starting at a very early age are ripe for exposure to folk music.
Advise: make it as interactive as possible. Musical games that include hand motions/body movements are winners among little ones. Making homemade instruments is exciting to kids, and they have something to take home and treasure. (Max has provided us with a nifty link at the top of each page "kids" where you can find patterns for making instruments.)
The rewards for doing this are multiple - primarily the sheer joy of participating with kids! It's a kick! They have the best questions about instruments.
A treasure of mine is a white Hanes T-shirt that each kid in my boy's classroom drew on in permanent colors. One kid drew a picture of my banjo, one drew a music staff with 4 lines and notes on it, one girl drew her dog and cat. It was given to me as a thank you for making music with the class. I'm so proud of that shirt and of the kids' enthusiasm for music.
Go for it, Sean. I doubt you'll ever regret it.
All the best,
Jeff