PROPOSITION 1: God is the Founder of all families: therefore families should pray unto Him. 

The household society usually is of these three combinations: husband and wife, parents and children, masters or servants: though there may be a family where all these are not, yet take it in its latitude, and all these combinations are from God. The institution of husband and wife is from God (Gen. 2:21-24), and of parents and children, and masters and servants. And the authority of one over the other and the subjection of the one to the other is instituted by God and founded in the law of nature, which is God's law. The persons, singly considered, have not their beings only from God, but the very being of this society is also from Him. And as a single person is therefore bound to devote himself to the service of God and pray unto Him, so a household society is therefore bound jointly to do the same because a society it is from God. And hath God appointed this society only for the mutual comfort of the members thereof or of the whole, and not also for His own glory, even from the whole? And doth that household society live to God's glory that do not serve Him and pray unto Him? Hath God given authority to the one to command and rule and the other a charge to obey only in reference to worldly things and not at all to spiritual? Only in things pertaining to the world and in nothing to things pertaining to God? Can the comfort of the creature be God's ultimate end? No: it is His own glory. Is one, by authority from God and order of nature, paterfamilias, “the master of the family,”? so called in reference to his servants, as well as to his children, because of the care he should take of the souls of servants and of their worshipping God with him as well as of his children? And should he not improve this power that God hath given him over them all, for God and the welfare of all their souls in calling them jointly to worship God and pray unto Him? Let reason and religion judge.

PROPOSITION 2: God is the Owner of our families; therefore they should pray unto Him.

God being our absolute Owner and Proprietor, not only by reason of the supereminency of His nature, but also through the right of creation giving us our being and all we have, we ourselves and all that is ours (we and ours being more His than our own) are unquestionably bound to lay out ourselves for God, wherein we might be most useful for our Owner's interest and glory. Whose are your families, if not God's then? Will you disclaim God as your Owner? If you should, yet in some sense, you are His still, though not by resignation and wholly devoting of yourselves to Him. Whose would you have your families to be “God's own or the devil's own”? Hath the devil any title to your families? And shall your families serve the devil, that hath no title to you either of creation, preservation, or redemption? And will you not serve God, that by all this hath a title to you and an absolute, full propriety in you? If you will say your families are the devil's, then serve him. But if you say they are God's, then serve Him. Or will you say, “We are God's, but we will serve the devil”? If you do not say so, yet if you do so, is it not as bad? Why are you not ashamed to do that, which you are ashamed to speak out and tell the world what you do? Speak, then, in the fear of God. If your families, as such, be God's own, is it not reasonable that you should serve Him and pray unto Him?

 Proposition 3: God is the Master and Governor of your families. 

Therefore, as such, they should serve Him in praying to Him. If He be your Owner, He is your Ruler too: and doth He not give you laws to walk by and obey, not only as you are particular persons, but as you are a combined society? (Eph 5:25-33; 6:1-10; Col 3:19-25; 4:1) Is God, then, the Master of your family, and should not then your family serve Him? Do not subjects owe obedience to their governors? “A son honoureth his father, and a servant his master: if then I be a Father, where is mine honour? and if I be a Master, where is my fear?” (Mal 1:6) Where, indeed? Not in prayerless, ungodly families.  

Proposition 4: God is the Benefactor of your families.

Therefore, they should serve God in praying to Him and praising of Him. God doth not do you good and give you mercies only as individual persons, but also as a conjunct society. Is not the continuance of the master of the family, not only a mercy to himself, but to the whole family also? Is not the continuance of the mother, children, and servants in life, health, and being, a mercy to the family? That you have an house to dwell together and food to eat together? do not you call these family-mercies? And do not these call aloud in your ears and to your consciences to give praises to your bountiful Benefactor together and to pray together for the continuance of these and the grant of more as you shall need them? It would be endless to declare how many ways God is a Benefactor to your families conjunctly; and you are shameless, if you do not conjunctly praise Him for His bounty. Such an house is rather a sty for swine than a dwelling-house for rational creatures.  

May not God call out to such prayerless families, as to them in Jeremiah 2:31? “O generation, see ye the word of the Lord. Have I been a wilderness unto Israel? a land of darkness? wherefore say my people, We are lords; we will come no more unto thee?” Hath God been forgetful of you? Speak, ye ungodly, prayerless families. Hath God been forgetful of you? No! Every morsel of bread [which] you eat tells you, God doth not forget you. Every time [that] you see your table spread and food set on, you see God doth not forget you. “Why, then,” saith God, “will not this family come at me? When you have food to put into your children's mouths? when they do not cry for bread, you are constrained to say, 'I would, my poor hungry child! I would, but I have it not!'” Why then will you not come at me? Live together and eat together at my cost and care and charge, and yet be whole months and never come at me? And that your children have reason, raiment, limbs, not born blind, nor of a monstrous birth, and a thousand ways besides have I done you good, may God say, “Why then will you live whole years together and never together come at me? Have you found one more able or more willing to do you good? That you never can. Why then are you so unthankful as not to come at me?”  

You see, when God is a Benefactor to a people (and there is the same reason for families) and they do not serve Him, what monstrous wickedness it is! God hath kept you all safe in the night, and yet in the morning you do not say, “Where is the Lord that did preserve us? Come, come, let us give joint praises to Him!” God hath done you and your families good so many years; and yet you do not say, “Where is the Lord that hath done such great things for us? Come! Let us acknowledge His mercy together.” God hath carried you through affliction and sickness in the family: the plague hath been in the house, and yet you live the smallpox and burning fevers have been in your houses, and yet you are alive your conjugal companion hath been sick and recovered, children nigh to death, and yet restored and for all this you do not say, “Where is the Lord that kept us from the grave and saved us from the pit? That we are not rotten among the dead!” And yet you do not pray to nor praise this your wonderful Benefactor together. Let the very walls within which these ungrateful wretches live be astonished at this! Let the very beams and pillars of their houses tremble! And let the very girders of the floors on which they tread and walk be horribly afraid! That such as dwell in such an house together go to bed before they go to prayer together! Let the earth be amazed, that the families which the Lord doth nourish and maintain are rebellious and unthankful! Being worse than the very ox that knoweth his owner and of less understanding than the very ass (Isa. 1:2, 3).  

From what hath been said, I reason in this manner: if God be the Founder, Owner, Governor, and Benefactor of families, then families are jointly to worship God and pray unto Him.

From “How May the Duty of Family Prayer Be Best Managed for the Spiritual Benefit of Every One in the Family?” Puritan Sermons 1659-1689, Being the Morning Exercises at Cripplegate, Vol 2, Richard Owen Roberts, Publisher.