I want to get my 8-year-old son a phone and I see the same problem. My dream would be that I could put a password on calls to him - that is, if somebody phones

I want to get my 8-year-old son a phone and I see the same problem. My dream would be that I could put a password on calls to him - that is, if somebody phones him not on a whitelist, they get a request for a PIN. If they can't do it, it gives them my number.