Sirius in Prisoner of Azkaban mentions that Wormtail intentionally sought after a wizarding family to take him in so that he could keep an ear to the ground regarding any news of his old master Voldy.
We know that Wormtail belonged to Percy before he was Ron's, but I cannot find any canon stating how he came to be with the Weasleys. There are a few possibilities:
- Wormtail Apparated close to the Burrow, turned into a rat and then what? Just waited around for the good-natured Weasleys to find him and take him in? I don't see it as being a logical jump.
- The other possibility is that he was taken in to the Magical Menagerie and the Weasley's just happened to buy him, rather than an owl or other magical creature that was allowed at Hogwarts. It could have been any wizarding family and just convenient that it was the Weasleys.
Both seem to be far fetched, but possible. is there any canon stating how he came to be with the Weasleys? from Prisoner of Azkaban - Lupin says that Wormtail had been part of the Weasleys' family for 12 years, i.e. within months of his disappearing act, how?