At least once a month, I will have them observe and sketch their tree in their nature notebooks.
One of our trees appeared about the time DS5 was born so we have always called it his tree. Of course that is the tree he wanted to journal this morning. Even though I have studied this stuff and seen it a million times, it amazes me when a child of 5 years produces something like this. It's amazing what they can do if we let them.
DS5's tree and sketch
DD10's tree and sketch