Signing into iCloud e mail on windows 10

Hi guys.

Ok I’m having fun & games with my sons windows 10 laptop unfortunately he has to have one for school work😬

he does have an iCloud account/e mail & it is a child’s account I am the organizer.

I know I can create a app specific password in my Apple ID in a browser but his Apple ID does not have that option.

I am trying to put his Apple ID password he usually uses into the mail app on his windows device but it just keeps saying attention required.

the iCloud windows control panel will only let me set it up in outlook but of course Microsoft want to charge you for that.

I have a feeling this is to do with it being a child’s account is there anything I can do to get round this.

thanks in advance guys.