You can easily block calls from unknown numbers using the built-in Phone app.
Here is how to set it up:
Open the Phone app.
Tap the three-line icon located near the search bar (usually in the top-left).
Go to Settings > Blocked numbers.
Toggle on the switch for Unknown (or "Block calls from unidentified callers").
Please note, this isn't a specific SafetyMode feature, rather, it is a feature built into the phone. This means it is possible for your child to turn off this setting.
