Among the Hidden - Margaret Peterson Haddix

Following the futuristic storylines of "1984" and "Brave New World" comes "Among the Hidden". Luke is a third child in a family with already two boys. This is breaking a decree established by the government. He's successfully hidden in his parent's home without discovery for 12 years, but a stray glimpse through an air vent reveals his prohibited existence. Does this spell freedom from secrecy?
In a future where the Population Police enforce the law limiting a family to only two children, Luke has lived all his twelve years in isolation and fear on his family's farm, until another third convinces him that the government is wrong.