Roughly four million American-born children have at least one parent who is in this country illegally, and life for these immigrant families can be complex. Immigration status determines who can work and drive a car, as well as who can leave the country to rush to a dying relative’s bedside. The situation is at the heart of the debate over immigration reform. Advocates are pushing for a way to keep families together; opponents say people should not be rewarded for sneaking across borders.