The Fall of Freddy the Leaf or other books make nice introduction to the subject of fall leaves and why they come off the trees.  There are also a variety of art activities that can be extenders on this subject.  I have my movement kids practice making shapes with their bodies and talk about how some leaves are wide, some skinny, some with rounded lobes, and some with “pointy” ends.  Then, Iet the “leaves” blow back and forth on their pretend trees until the wind finally blows them to the ground.  Since leaves don’t have knees, feet, legs, or arms, they can only roll around.  Then I pretend to “rake” them up into a pile.  But of course, when I pretend to go get a leaf bag to put them in, the “leaves” always blow away!  (A big kid favorite!)