I think my son was 2 when I discovered this. To to youtube. Type in a random thing of interest, like "fire truck". And then watch videos about that topic.
Of course things have progressed since then. My son is almost 5 now. And he just discovered dinosaurs. So we watched some dinosaur videos yesterday and discovered the series of "Walking with ..." series. And as these things go, I wound up going to Amazon this morning and ordering several series. Walking with Monsters, Walking with Dinosaurs, Allosaurus, A Walking with Dinosaurs Special, Chased by Dinosaurs and Walking with Prehistoric Beasts. (Yeah, overboard. But I know my son and it is a good price.)
Yes, I know how much they made up. But there is a lot of good science in there as well. And I know how much my son will love it.
Now lots of people, including many copyright holders, think that youtube is a horrible violation of copyright. Technically they are right. But I believe that there are plenty of people like me out there, and the net effect is more people discovering then buying things they like. Which is good for copyright holders.
And it is a belief backed by some evidence as well. For instance look at the Baen Free Library. Put books online for free in multiple formats and what happens? Sales go up!