Creating fall leaf pictures is a classic craft activity that can be enjoyed by all ages. You'll find this lovely example and others at Atelier Pour Enfants.
4 Ways to Make Self-Portraits with 3 to 5 Year Olds
Heimische Blattformen / Bäume bestimmen by Iris Luckhaus
kids love to do these - good to tie in with plant units in science - plant collage animals
collage natural items onto photos of your kids to make them crazy costumes
Easy, Fun DIY Activities You Can Do with your Kids - Petit & Small
Make and Decorate Your Own Nature Paper Dolls by Mer Mag