Comment to Do you know that UNA...
Anything related to kids can be tricky - it has to be done with parental controls and reporting to comply with various codes. We did a few setups for schools.
Yes, you can create a network of UNA-powered sites using UNA Connect module for single-sign-on.
May I ask, what the idea behind creating this module was?
By installing "UNA Connect" on site1 and installing "OAuth2" on site2, then configure them, you can login to site1 using credentials from site2.
This is a feature that has many applications. I need to sit and think this through.