Here's an interesting article about cohabiting versus marriage and the subsequent results for the children which result from it.
Now, I may be more eager to believe it because it agrees with what Scripture says regarding marriage. On the other hand, this does not vindicate God's design for marriage. God vindicates himself. And his word is clear: "Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous." (Hebrews 13:4, ESV) In other words, the marriage bed is a good thing, and sex within marriage is pure. Outside of marriage, sex is "immoral," "adulterous," and "defiled." This is God's judgment of it. We ignore and defy God and his word at our own peril.
What's more, the article above states that studies now prove that children born outside of marriage are raised in homes that are not as stable and that it has a negative effect on children. Better for the children is that a husband and wife be married, commit themselves to one another, and serve as dutiful parents who love and discipline their children.
It is as if God were on to something when he designed marriage, sex, and child-rearing in the order he does!