Check out some of the resource books on my bookshelf:
Brick Science: STEM Tips and Tricks for Experimenting with Your LEGO Bricks―30 Fun Projects for Kids!
Making and Tinkering With STEM: Solving Design Challenges With Young Children
Cardboard Box Engineering: Cool, Inventive Projects for Tinkerers, Makers & Future Scientists
Build Your Own Chain Reaction Machines: How to Make Crazy Contraptions Using Everyday Stuff--Creative Kid-Powered Projects!
Crazy Contraptions: Build Rube Goldberg Machines that Swoop, Spin, Stack, and Swivel: with Hands-On Engineering Activities (Build It Yourself)
Save the Crash-test Dummies: An Action-Packed Journey through the History of Car Safety Engineering
Making Simple Robots: Easy Robotics Projects for Kids Using Everyday Stuff