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.
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.