This is 100% a sign of the parents, especially the fathers
For example, in my parish, there are approx 90 kids per “grade” from first grade to 6th for Religious education (we confirm in 6th grade).
But there are NO where near that number who attend Mass on Sunday (our Religious Ed programs for kids are on Tuesday & Wednesday nights, without a Sunday option)
There are many people who bring their kids to Child Faith Formation classes, but never bring their kids to Mass (except maybe on Easter or Christmas). Perhaps the parents promised their own parents that the kids would receive the sacraments, or something … so they bring them to Child Faith Formation, but not to mass.
In my parish, I don’t know what the % is, but in speaking to many of the Catechists, I know it’s a large number of the kids.
Our parish also has a pre-school, and a large number of them do not attend Mass, and same with the regional Catholic elementary school… most of the kids who attend the regional Catholic Elementary School are from my parish and a majority of them do not attend Mass on Sunday.
Why? Their parents.
So these kids are not leaving the faith on their own, per se. Their parents taught them nothing of the faith, no love of the faith, no love of God, etc… They just see Church as extra schooling. If they are not coming to mass, then it’s a safe bet that there isn’t any Rosary at home, no Grace before meals, no Confession, etc.
13 is a good average age of when Confirmation takes place… and many kids who have parents who don’t attend Mass will rarely ever attend Mass after their Confirmation (which is very sad).
Further proof of this, I was in a used book store, where I have seen at least twice Confirmation gift Bibles with kids names written in them… the Bibles were in the used book store only 2-4 years after the kid’s confirmation
When I was a kid, CCD was considered a “lab,” you main faith formation was in your house. But I was born in the late 1970s, grew up in the 1980s and early 1990s. So my parents knew very little, and my dad never attended Mass.
The only way to fight this is with hard nose faith formation, esp for the boys. Because, as the start of my post hinted, if dads are not engaged in their faith; chances are VERY high that the children will not be either.