I watched Alec Baldwin on MSNBC interview the two actors who played astronauts in 2001: A Space Odyssey. Learned among other things that the music for the movie was originally put on there temporarily so they've have something on there when they showed it to test audiences. They paid to have original music composed and recorded then liked the temporary stuff so well they decided to keep it.
According to a documentary about Harry Nilsson, this was how "Everybody's Talking" got to be the theme to Midnight Cowboy and it's old news that this was how they selected the music for Easy Rider.
Similarly, there was the shot in the movie Lawrence of Arabia. Peter O'Toole holds up a lit match. We expect him to put it out with his fingers, but he blows it out and the picture cuts to a shot of the sunrise over the desert. The script called for this transition to be done in a long dissolve. Had it been edited on a computer, this is probably how it would have ended up, but because they edited on film and the dissolve would have to be added later with an optical printer, they saw how good it looked as a direct cut and stayed with it that way.
There there was the movie Snakes on a Plane. They didn't have a real title, so they put that crude description on the script until they could think of one. And they decided that was about as good as it was going to get. I haven't seen it, but I hear that the title may have been the best thing about it.
I don't really have a point here. I was just watching a documentary about Harry Nilsson and they mentioned the thing about "Everybody's Talking".
Nilsson was born in 1941. His father was in the Navy and he grew up thinking he had been killed in World War Two. Then he discovered in the '60s that he was alive and well and was married with a family in Florida.
It always comes as a shock. Both Jack Nicholson and Bobby Darin learned as adults that their much older sisters were their mothers and that their parents were actually their grandparents. Lars von Trier learned that his father was actually his step-father and that his biological father was a German guy. It was a good thing his mother didn't tell him----she wanted a child with the German guy because he was from a creative family. She wanted creative genes for her child. If Lars had known, he wouldn't have reacted against that and become an accountant or a gas station attendant----both occupations that are far more useful than movie directors.
It's probably a good idea to tell the kids the truth. Within reason. Don't mention botched attempts at contraception or alcohol playing a role in their conception like John Lennon did talking about Julian.