I told the kid (about 10 yo at that time) of friends about the can-string-can phone and we made one. I didn't expect that he would play with it for more than a few minutes. But to my surprise I noticed on later visits that the string phone was used when playing with friends. I've even noticed that it got repaired or even rebuild at some time.
However, I think that he would never have learned about it if I didn't told him. Many parents are not enough involved with their kids to tell them about (or point them to the right books, web sites, ...) about these easy to try experiments.
Most kids would love to do these kind of experiments, but they need some guidance to get started. But it's easier to just give them a game console so they ask for even more parent's attention :-(