Blessings to you for this warning. I'm going to do something about changing the location of this mailbox asap.
An email account! It makes sense for YouTube maybe, and I suppose the problem is it's all intertwined? But then there's Android too - is it really expected that if you're a (say) 10 year old whose parents think is old enough to have a phone (let's not debate that here) is it really expected that you skip the set up with Google account flow on Android first boot? Because it's very clearly not the preferred path; one they don't really want you to take.
Seems like 'underage' accounts should just have restricted access, i.e. none to whatever it is (like YouTube) that's the problem, I can't believe it's email.
Correction: technically a Chrome ad, yet very heavy use of Gmail. Maybe the trick is to not open it in their exact name? (In the ad they use "dear{name}@gmail.com)
I use fastmail and have been sending emails to my young sons “email”, which is just a subdomain of my personal email, so I guess technically it’s not his but I have a way to share all the mail with him.
This incident is exactly what precipitated my switch to Fastmail.
Unfortunately, I did it by making them gmail accounts. Google without warning closed both accounts when my daughter was 12 for being under-age. I lost everything. I tried to appeal to get them to unlock the accounts long enough for me to get the contents out, but talking to a human being at Google is famously impossible.