Sorry I am late to reply. User Limnos gave a great response. I just wanted to add a couple more items in case it wasn’t clear.
For tech companies managing protection for children via their guardian vs. protecting children's privacy is a very big grey area.
Children under 13 can have their iMessage, Contacts, and other very private areas controlled by their guardian. After 13 they can create an Apple ID on their own. If under 18, you can add them to the family group with the ability to control the areas mentioned but not everything they do.
This article talks about setting up an iOS device. Help your child set up an iPhone, iPad, or iPod touch - Apple Support
If this is on a macOS device, I suggest first setting it up using your Apple ID. By default you will be an Administrator level user of the device. You could then create a standard level user account for them to use with their own Apple ID.
Set up users, guests, and groups on Mac - Apple Support