"Cross my heart."
I took a deep breath, signalled Ruth to make some coffee, and began.
"You were right about Santa Claus, Adam. He's just make-believe, and so are the fairies. Santa Claus was invented by Mommies and Daddies to represent the spirit of Christmas for kids too little to understand its real meaning. People on Earth still observe the holiday, although they've gradually forgotten what it really stands for. I'll explain that part to you later."
"What's Earth, Daddy?"
"Earth is where everybody lived before there were any spaceships. It's a big place, and some of it's nice and some of it not so nice. The people live in houses, something like this one, and the ones in a house are called families. There's a Mommy and a Daddy for each family, and their kids live in the house with them."
"Where do the kids come from?"
"From the Mommy. It's the same as what we call 'making a Dolly'."
"Oh."
I talked for six hours, until I was so hoarse my voice was cracking on every other word. He took it all in stride, injecting a question here and there, absorbing it all like an unemotional sponge. But when I began to talk about war, he became a little upset. I explained how it had begun as individual struggles for survival or supremacy in the days of the cavemen, how it had evolved along with society into struggles between families and tribes, then nations, and now—between planets.