When she was five, my niece believed that in the "olden days" folks had all the stuff you saw in movies - horses and carts etc - but that they also had TVs and computers. Maybe she believed that the movies of the past were docos and so they had to have TVs in order to film the movie?
A childhood belief about history

others believed things like this
- I used to believe that the olden days were black and white when I was about 3 from seing old movies.— Sam
- I used to beleive that in order to rewind a film the actors would have to re-act the whole movie backwards. — movies backward
- I used to think actors in movies sometimes had to actually die to make the movies look real.— Dero
- I used to think the olden days came once every couple of yearsAnon
- My brother believed that bacon(his favorite food) was from horses. — Jenn
- I believed when young that horses with white faces were sick. My dad a great sense of humour— John Cavanagh