Make a solar cooker: https://www.homesciencetools.com/article/how-to-build-a-solar-oven-project/

Build an Air-Powered Car: https://gems.education.purdue.edu/wp-content/uploads/2019/01/aircarfromzoom.pdf

Build a Hand Crank Winch: https://littlebinsforlittlehands.com/build-a-winch-simple-machine-recycled-stem-activity/

Make a Water Filter: https://tryengineering.org/wp-content/uploads/filtration.pdf

Exploratorium The original hands-on, creative STEM museum has wonderful videos and activities for all ages.

Try Engineering (4-12) lots of amazing resources and activities