Can't set up child's login because it keeps sending a code to its email.

I am trying to set up my child to login on my laptop and play games.

I've had to set up an email address for them to do this (I did not want to do this, he's 5 he doesn't need an email account)

So I follow the instructions and set it all up, and it tells me to login to his account to finish.

When I go to login to his account it says it has sent a 1 time code I have to type in.

I cannot access his email without leaving the page on the device, logging back into my account and going to his email. Which doesn't work because it generates a new code when I go to login on his account again.

So do I have to set him up on two devices (which requires downloading the family app and more one time codes) so I can see the email account I've had to make for him on one to be able to login to another, just so he can use a laptop?

Is this overly complicated or am I missing something here? Can I not set their password from my admin account?