set up child account and user on mac

I am trying to set up a user on a new Mac Mini for my child, with Screen Time options, and can't for the life of me figure out how to do it, even after looking through the documentation.

What I have done so far:

1) Set up Family Sharing and created an Apple ID for my child.

2) Created a Standard User for my child on the Mac Mini (I am the administrator).

What I haven't figured out how to do, nor found documentation for:

1) How to link my child's user on the Mac Mini to their Apple ID.

2) Select my child's user in Screen Time setting to set it up.

Any help would be appreciated.