Jenga, LEGOS, K'NEX...Barrel of Monkeys...Kerplunk? The list goes on! And yes, I grew up in the '70s.
Here's an activity you can try with just a few household items:
1) A few items to stack or pick up or move: cups, blocks or socks etc.
3) String or ribbon
Ask your big or little engineers this: "How can we move these items without touching them with our hands? How can we move them or stack and unstack them using only rubberband(s) and/or string? How can we do this using the help of at least 2-3 people?"
Have fun! (Don't share the photo until you've tried other designs.)