But it’s not putting emphasis on the marriage at the expense of the children… it’s putting that emphasis there for the good of the children. The CCC defines it this way…
***1641 "By reason of their state in life and of their order, [Christian spouses] have their own special gifts in the People of God."147 This grace proper to the sacrament of Matrimony is intended to perfect the couple’s love and to strengthen their indissoluble unity. By this grace they “help one another to attain holiness in their married life and in welcoming and educating their children.”***148
1642 Christ is the source of this grace. "Just as of old God encountered his people with a covenant of love and fidelity, so our Savior, the spouse of the Church, now encounters Christian spouses through the sacrament of Matrimony."149 Christ dwells with them, gives them the strength to take up their crosses and so follow him, to rise again after they have fallen, to forgive one another, to bear one another’s burdens, to “be subject to one another out of reverence for Christ,”…
The gist being that marriage is a sacrament through which grace flows to build and sustain in the difficulties and burdens that will come in living together and raising children. So as with the airlines instructions to fit your oxygen mask before you fit your childs mask… there is a fundamental recognition of the value of your marital health in the health of the children.