Restrict "Find My" on kids' iPad
I took some time to research this.  It doesn't appear that you can disable 'Find My' using the Apple Parental Controls.

It seems strange to me that this isn't possible but I couldn't find any authoritative way to prevent changes in this app.

Using the regular Parental Controls on your child's iPad allows you to prevent changes to many system settings and apps so I would recommend doing that, at a minimum.  Also, there might be 3rd-party apps that provide more granular control, for a price, but that's a space that I don't know much about.