Dear (oldest) son,
20 years from now, when you think you've found the right person to spend the rest of your life with, do you think you will remember that you said this when you were 3? Because I know I won't forget!
"Daddy? If a girl asks me to marry her, I'm going to say no. Because I already have a family."
Seriously - that's fine by me, big boy. I'll even buy you a house next door to mine. And one for your brother, too. So you boys can live next door to me, a la My Big Fat Greek Wedding. Because that would make me very happy!