I work on teams adjacent to those responsible for the QR code you encountered while creating a Google account for your child.
The screen you saw, I assume, was something like the attached screenshot. Firstly (and most importantly) as mentioned in the highlighted section your details are not saved to your account, aka "not persisted".
So why does this exist at all? You folks touched on the core issue - abuse. Free Google Accounts are often created at scale to create nuisance, and more. Trust me, I/we pine as much for the simplicity of the good old days as you folks. But some things are just gone forever.
Finally, as a parent of a 10 yr old myself, I strongly encourage you to create a child account, which gives you some supervision and parental controls. You are anyway using a fake date of birth for that user; why don't you just make it a "Fake but Minor" DOB instead? Trust me it is worth the little extra hassle.
