How do I block an app on my child’s phone

Settings>Screen Time(Turn on if not on already)>Use Screetime Passcode and set up any code you would like>App Limits>Add a limit> Pick an app>Then set a time limit(0mins 0 sec to fully lock with typing passcode every time)

Try setting it to 1min, I don't think Apple personally can block it until you turn in off unless you get some Third-party application.

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