One of them has light hair; the other dark. They both have blue eyes. They both are eight years old. They keep each other's hand, tightly. It's the most important day in their lives, but they aren't nervous.
They've got each other.
Then a tall man approaches and separates them.
They look into the Vortex, alone, and everything changes.
One of them runs, runs as far as his legs would carry him. The Vortex is powerful and terrifying. He doesn't want this.
The other steps closer and closer. The Vortex is beautiful, tantalizing, hypnotizing... He reaches his hand out to touch it.
They are both stopped by adult Time Lords at the same moment, but it's too late. They are brought back together, as if nothing has happened - but of course everything's changed, and they may only pretend it hasn't.
In nine hundred years, they won't be able to do even this.