Yesterday I told my kids that you can write any number with ones and zeros. They told me this was impossible.
So I showed them the binary number system using the same setup they had used for the base 10 number system. They told me it didn't make any sense and it was impossible.
Then I drew a picture of me and them separated by a river. I wanted to communicate numbers to them across the river and all I had was a box with light bulbs mounted on it. After two examples (of communicating their ages), they completely understood and started working out how I could send other numbers.