Sounds like a lot of fun!
SO think dimensionally. Start below the ground with mycelium and food/healing roots. This encourages thought and makes things even more magical because kids will start thinking about what living things they may be walking on. Move to forest floor where the action of seeds and nuts happens, then upward.
Above ground is the easy part.
Maybe an area of your project can be devoted to the poisonous/noxious plants and mushrooms. Not to play with but to learn to identify for safety purposes.
Of course you will need an area where they can move dirt with impunity and prospect for what dwells beneath.
So much is learned from observing nature.
I have always loved maple syrup time because being in the bush as a child taught me the order things wake up in, and in the fall while hunting I learned the order they go to sleep.
Dad taught me about mushrooms and tracking and foraging from the time I could keep up on the trails.
Nature has stiff rules. You can count on them.
A child will never forget what they learn in the bush.
Best of luck!
