To add a data point, my kids are not allowed on any social media and don't have phones. (They have iPads, but they are locked down and blocked at home anyway)

But that doesn't stop them seeing things on social media - when they are at the park, there are always peers there that have a phone and showing TikTok videos or Facebook reels etc, so even though I, as a parent, have blocked it at home, and chosen to not give them a smart phone, they are still exposed to it outside of that.

(And to be be fair, the same happens to me in a way. I don't have any social media logins, but I still get sent links for Instagram/FB/TikTok from friends, or my wife will show me something she's seen there, so it seems there really isn't much escape from it!)