Send anyone who does not yet have a VDS account an invitation to play!
Let your friend know that you'd like to be their Sire in the game. If they accept your invitation, they will see that you are an option to choose as a Sire when they begin the game. If they pick you, they would be your childe and you would be their Sire.
Another way you can become a Sire to someone is through the "Adoption" feature.