Why can’t children sign in with their Apple account?

I have seen this error too. It is when your kids want to create an account in another app or service and it provides an option for sign-in with Google / sign-in with Apple / others. Kids under 13 cannot use this sign-in method. If they could it would make life much simpler for parents. So now, the kids need to create separate accounts and passwords for these apps/services.

Here is the page from Apple showing these details:

What is Sign in with Apple? - Apple Support

"Sign in with Apple is not available for children under 13 years old. This age may vary by country or region. This age restriction doesn’t apply to Managed accounts."

Sign-in to what/where ?

Their Trusted Device are presumed to be always signed-in to their Apple Account.

This seems an entirely reasonable - and parental empowering - approach for Apple to take.

Children creating their own “unsupervised” logins at random websites might appear to be the more pressing problem.