Is there a way to prevent child from adding contacts on Apple Watch SE?

I set up the Apple Watch for a child. The number appears to have been recently in use by someone else because it gets numerous text messages from people not in contacts. The watch shows the number or email address from which a message was received, but will not show the message because it is not from an authorized contact. Perfect. HOWEVER, the child can simply ADD the number or email address to their contacts on the watch and then view the messages!! That’s ridiculous. And as yet, I cannot figure out a way to prevent the child from adding contacts via the watch. Does anyone know how to do that? Because if you can’t, the Family Settings parental controls are worthless.