Here's a quote from the first episode, where Carol is explaining to Stephen what it means to be a Tomorrow Person:

Carol: Perhaps every child is a Tommorow Person but doesn't realise it, or is too frightened to.

Stephen: Couldn't you tell them?

Carol: No, we have to wait until they call us, like you did. Then we can take over, stop wars and put the world in order.

Stephen: Us children!?

Carol: Oh yes. You see, we are man's only hope of survival. We're peaceful, we can't wage wars. And we can't kill...

Of course, the world didn't work out like that. Still, would have been nice