Happy first day of fall! While I'm personally not looking forward to raking all of the leaves that will soon be falling at my house, I don't mind an autumn-themed music lesson centered around a fun book for my early childhood students. Patterned after "We're Going on a Bear Hunt", this book by Steve Metzger is a great introduction to the fall season for your youngest students. "We're Going on a Leaf Hunt" lends itself well to many musical extensions.
Do you have access to an Ellison die-cutter? If so, you can use it to cut out the various colored leaves you will need for this lesson. If not, you can develop your own leaf pattern; I recommend using google image.