I LOVE doing this with the kids each year. It's my favorite yearly activity. This year, I had the littles create a tree using leaves from their nature walk last week and then they got to paint a trunk on the tree (I outlined it so they knew where to paint). I've had issues with things this big sticking to the walls thanks to the paint we used on the walls (glossy and easy to clean because, kids), so we stuck it to the door using Magformers. It's in the perfect place for us all to look at it in the daycare and read the leaves.
I love what the kids came up with for the littlest littles who can't talk yet and the toddlers had amazing answers (likely thanks to hearing what the five year old was thankful for!).