I am looking for a book I read a long time ago it's about a dystopian country where your only allowed to have 2 kids, but this family has a 3rd and they have to hide him in the attic and he can't go to school or do anything. I don't remember a lot, but I think there was a family that took him in after.
I remember a TV show with that premise: Terra Nova. But the third child was a girl, and they were in the dystopian future for only one episode.
Idk if it's what you're looking for but I remember a book called, Among the Hidden by Margaret Peterson Haddix it's the first book of the Shadow Children series. MC is the third child he makes friends with the next door neighbor's third child as well and I think he comes from a low middle class background bc for some reason potato chips are a luxury for him to eat. Idk if he goes to another family it's been a long time since I read it.