My Apple ID is used on a new device but it doesn't say in what location or device

Dear all!

I get almost every couple of weeks nowadays a valid email from Apple, stating that my child's AppleID was used to log on a new device. The email comes from: noreply@email.apple.com which I checked is valid.

My child is in my Apple Family, I'm the organizer, so his account is under mine.

However, no new device, or technical device information, is shown in the email. Log in time, in UTC, is shown, but no location.

Also my child, school-age, says that he has not received those two-factor authentication messages / approvals / number series, required for new log-ins... And nor do I get those to my phone (cause I can also confirm his log-ins as the parent).

His AppleID should be in super safe hands, and only I, as an adult, know the password.

What can this be about? What triggers these emails? I do not understand why these are generated.

The phone is used only for phone calls, texts, and Whatsapp, and some googling. No games, no log-ins, no other apps.

I then change the password, just in case, and always make sure to log out from all devices as changing passwords. And when I log in, on my own laptop, I get all the normal two-factor codes and approvals to my & my kid's phones. This is weird!

Thank you if anyone can know what this is about!

[Re-Titled by Moderator]