The wizarding war ended, the dark lord had lost. All the death eaters were placed in Azkaban, all except the children of the dark families. The death eaters below the age of 18 - with and without the dark mark - were not facing charges. But they were required to stay with "normal" wizarding families to teach them the good/normal way to act in the wizarding world. Just your luck... you are placed with the Weasleys.

Molly Weasley opens the door with a large smile. "Ah, hello dear. Come on in!"