I use Cookie AutoDelete on Firefox and it's great. It works with Firefox Container Tabs (groups have their own cookie settings), and let's you greylist (allow cookies from a particular domain pattern until the tab is closed) or whitelist (always allow from the domain pattern). I set it up for my kids computers also. The default is to blacklist (cookies aren't set), and I can whitelist for particular sites where they need say persistent login.

Definitely in 2026 kids should be getting tons of education in public school about how to safely browse the internet, both for personal data privacy and for safety against stalking, doxxing, grooming etc in the same way millenials were grilled about source checking internet resources like Wikipedia.