Don’t worry, we’re already doing all the typical toddler games and I’m not keen on raising a STEM child prodigy. That’s why I asked for hands-on experiences with prodcuts specifically for toddlers.
I really like the cardboard approach. Maybe I can come up with something on a plywood basis. Copper tape is a great idea. Also thanks for the link, I imagined something like this just a little bigger and sturdier and with more basic components (resistors included with the LED for example). Will save the book for later.