In January Barna released a study which claimed "Generation Z" (born 1999-2015) is the first "post-Christian" generation. "More than any other generation before them, Gen Z does not assert a religious identity." The data then goes on to say 14% of GenZ is atheist, 13% is agnostic, 42% Christian (non-Catholic) and 17% Catholic (thus 59% Christian). One wonders how this can possibly be post-Christian.
A 2010 study from Pew notes the progressively less religiously affiliated nature of the generations.
But an important caveat is included in the Pew study:
Yet in other ways, Millennials remain fairly traditional in their religious beliefs and practices. Pew Research Center surveys show, for instance, that young adults’ beliefs about life after death and the existence of heaven, hell and miracles closely resemble the beliefs of older people today. Though young adults pray less often than their elders do today, the number of young adults who say they pray every day rivals the portion of young people who said the same in prior decades. And though belief in God is lower among young adults than among older adults, Millennials say they believe in God with absolute certainty at rates similar to those seen among Gen Xers a decade ago. This suggests that some of the religious differences between younger and older Americans today are not entirely generational but result in part from people’s tendency to place greater emphasis on religion as they age.
In other words, just because young people say they are non-religious today, doesn't mean they will always. It could be the Barna data is a function of their current age.
And there are other reasons for the change: it's likely not a change in the number who actually attend church, but rather a change in how those who are non-church-attenders talk about their lack of attendance. See this, and this with data from Rodney Stark (with chart back to 1974), about how the % attending weekly church services hasn't changed.
Also look at this "40-year-study that shows us what's different about GenZ" - but again, don't expect these things to be fixed in cement. Generations change.