Vampires are all kidnapped at birth
Hermione was kidnapped when she was born. Her real parents are vampires and one of them is a witch but Voldemort killed her mother and her father committed suicide because he was depressed about it. - Chapter 8
As the above quotes demonstrate, if you have a slight suspicion that you fit in with the vampires you`re probably kidnapped at birth. Your parents were actually vampires, but some damn muggles decided to go steal you from them. Because, you know, vampires would totally let their children get kidnapped by powerless muggles.
The future of a kidnapped vampire baby
You will end up going to Hogwarts School in England, where you`ll luckily not be on your own. About half of the current Hogwarts population are vampires. You will not be accepted as a proper member if you do not memorize all songs by My Chemical Romance and Good Charlotte, and have the scars on your wrist to prove you`re emo. Sorry, goff!
You have a lovely life of wrist cutting, french kissing, sex and eating cereals with blood ahead of you!