The family is, so to speak, the domestic church. In it parents should, by their word and example, be the first preachers of the faith to their children; they should encourage them in the vocation which is proper to each of them, fostering with special care vocation to a sacred state.
In hac velut Ecclesia domestica parentes verbo et exemplo sint pro filiis suis primi fidei praecones, et vocationem unicuique propriam, sacram vero peculiari cura, foveant oportet.
In The Splendor of Faith: The Theological Vision of Pope John Paul II (Crossroad, 1999; 2nd ed. 2003), Cardinal Avery Dulles writes (p146 of the 2003 edition, which I have read only on Google snippet view):
John Paul II has frequently repeated the term ecclesia domestica without adding the qualifier veluti ("as it were") used by the council.
Dulles' cited examples are Catechesi tradendae 68 (1979), Familiaris consortio 49-52 (1981), and Evangelium vitae 92 (1995). John Paul II's homily Expedit ut laborem (26 Sept 1980) also speaks of the family's place as "ecclesiola" seu ecclesia domestica; and his statement in Familiaris consortio 21 that
The Christian family constitutes a specific revelation and realization of ecclesial communion, and for this reason too it can and should be called "the domestic Church."
can now be found in the Catechism (s. 2204). A footnote in FC refers to Lumen gentium and to Paul VI's Apostolicam actuositatem 11 (1965) - which says that the family fulfils its mission "if it appears as the domestic sanctuary of the Church" (my emphasis; the Latin is tamquam domesticum sanctuarium Ecclesiae se exhibeat).
It's not hard to find bundles of sources for the family being a good thing, and support for its special role in education. But it seems, especially in FC, that John Paul II gives the family a theologically elevated position, as an explicit Church-in-miniature, and that this is a novel development - whereas previous authorities used the phrase more cautiously. Is this actually novel? I would be interested in finding earlier (pre-Council) sources for this theology, or alternatively an explanation of how it differs from prior explanations of the ecclesial role of the family.
(I should say that I don't have a problem with novelty, so this isn't intended to be a criticism! I'm just interested in the history of the idea.)