How do I prevent my child from using their iPhone hotspot?
So this is a question with an answer. I've seen so many parents ask this question, only to have the threads be closed so fast that it makes it hard to find definitive answers.
Currently, running IOS 16.2 as of May 17, 2023, Apple does not support the ability to disable the hotspot feature at the phone level. This is true even though the feature is nested under cellular data options in the menu system and that Screen Time has an option to prohibit modification of cellular data options. As many have pointed out, selecting don't allow does not have the presumed result of keeping your kids from completely bypassing ALL restrictions if they have a second device that then uses the phone as a gateway.
My feelings about corporate responsibility aside, the bottom line answer is that after elevating the issue with Apple Support, I was informed that it just simply cannot be done at the phone level. This matches mine and others user experience. The feature CAN be disabled by most carriers. Carriers are who you get your cell service (such as T-Mobile, ATT and Verizon in the US). Often 611 will get you right to them, but there are hundreds (if not more) so the contact method may not always be 611.
I really hope this helps, as this is a glaring security hole. As an aside, another feature that circumvents parental controls at router level is private MAC addressing. If you use parental controls on your router be sure to keep that in mind.
There are a lot of parents operating with a false sense of security based on the way Apple describes the cellular data lockout on ScreenTime. I strongly encourage you to provide feedback to Apple on this issue.