is that a growing percentage of folks don't think that sex before marriage is a big deal or that there is much wrong with having a child without being married, and certainly not a reason to be kicked out of school. As your linked article states, "The share of Americans who say sex between unmarried adults is “not wrong at all” is at an all-time high." This is the moral decline referred to.

The reduction in kids having sex today, as your linked articles point out, is not due to any cognizance of a moral code. There is an overall decline in "dating" overall, but kids are finding ways to "pleasure themselves" nonetheless.

Teen pregnancy would in fact be okay morally (law of chastity-wise) if the parents were married, although I don't recommend it. The decline in marriage rates and overall respect for the institution of marriage is another sign of things going in the wrong direction.

Yes, there is a definite decline in sexual morality as it is understood and taught by the Church.