I went to a public high school back when Mainline Protestantism was almost the “school religion”. Now, secular humanism is the official religion. But I didn’t become a Protestant, and I don’t think there is a good reason to think all children now succumb to the current “official religion” anymore than we did then. I now have a granddaughter who is in a public high school of necessity, because there are no Catholic high schools within driving distance. Not only is she not swayed by the “official religion”, she finds herself challenging it in her own thinking, just as I challenged Mainline Protestantism in mine.
At some point, all children confront the world. In my opinion, if they have been sufficiently catechised in the home, they will not succumb to the foolishnesses that abound in the secular world.