Laura Sessions Stepp of CNN Opinion reports on a problem of many Fundie churches. Once the kids are out on their own, they leave the church. There is a 43% drop in attendance by young adults. Many of this age do leave the church (and not just Fundie denominations), only to return 2-3 years later when they have kids of their own. But many are now marrying much later (if at all) so the gap could be 10 years. And with such a gap they are unlikely to return.
The reason for the big exodus is the young adults don't like the way the church is telling them to live their lives. They don't like being condemned for being gay, having sex outside of marriage, living with a partner, being a single mom, or opting for an abortion. This condemnation is much stronger than the sense of community they get within the church, so they leave.
Having heard of enough studies about kids doing better with two parents (the studies that get misused by Fundies who insist those parents must be of different genders) I think having kids within a marriage is a very good thing for the church to teach. However, I don't like the harsh condemnation for violating that rule.
That makes me wonder if the youth are rejecting the teachings on sex because they also reject the teaching on gays. Stepp doesn't provide any data. Of course, it is quite possible the culture's teaching on sex is much louder than the church's and that may be enough for the youth to reject the church's teaching.