We’re disagreeing not on the need to shield one’s children from objectively bad and harmful things, as I’m sure you’d agree that you wouldn’t want your kids visiting classmates homes who are operating a meth lab and who smoke and drink with their children.
We’re differing on what is harmful. I believe halacha decides what is harmful, and unfiltered internet, television, the potential for inappropriate mixing in with siblings of friends of the opposite gender, and food that might not be even kosher, all are individually enough of a reason to prevent unnecessary contact.
If you think those things are “petty”, well, “אם לחשך אדם…על תתגר במרעים, דע שאינו אלא מהם”