How to set up child's device so I can unlock it if it becomes disabled/unavailable?

Hi, I am legal guardian of my developmentally delayed child (age 21). She has her own device, an iPad. When I set up her device last year I set it up independent of mine. She has her own iCloud etc. However, there was a recent problem where she got locked out of her device when another child got ahold of it. So now I want to add her device to my account so that if that happens again, it will be easier to unlock the device. Do I need to add her device/ID to Family Sharing then? Will her info AND mine on Family Sharing (on her end) be private if someone gets ahold of her iPad? What is the purpose of "Family Sharing"? Also, how to add her device to Find My app?

Thanks.