Let history remember that today was the day my four year old son received his first ever explanation on evolution's course, and that the explanation came in the shape of the following clip from Carl Sagan's Cosmos:
Let the record also show Spotify is to blame for us getting to matters of evolution. We were listening to my favorite Vangelis tune, Alpha, when my son commented how boring it is; in retaliation I had to show him exactly why that music carries so much weight with me. Hence Cosmos.
By the way, over the last couple of days we have been discussing what metals are and where they come from (supernovas), compared to what plastics are and where these come from. I got to the point where explaining about the nature of the atom and how one element differs from the other seems the natural way to progress the discussion. Not that my four year old understands too much; I consider the general exposure the most important thing. Plus it's fun: it's fun to hear the questions and it's even more fun to think the answers up and try to present them in a comprehensible manner.