Home is the ultimate small group for growth and mission in this world. Think about it. Home life provides a context of discipleship unlike any other where parents serve as primary pastors to their children. Mark Driscoll writes,
Because parents love their children the deepest, know them the best, and are with them the most, they are best suited to be a child’s primary pastor who gospels them, teaches them, loves them, prays for and with them, and reads Scripture to them.
I would only add that the home ought to be a place where parents model a missional life to their children. But let's be careful not to go too far with this idea of home as a small group. Though it's true that parents are the primary teachers and shepherds for their children, it doesn't mean that the Church is secondary and unneeded. On the contrary, our temporary, earthly family is part of a bigger, eternal church family that reinforces and supplements the biblical instruction we ought to be giving in the home. Our home small group is not the church. It is part of the church, indeed, part of the body that grows and adds members through it's common mission.