How to change child age from 17 to 13 in apple family?

I am not an apple ecosystem user myself but I have a macbook from work and associated apple id.

Our son got an iphone when he was 12. For some reason, that I dont recall unfortunately, we had created his account with incorrect age (I think 16). We still were using the location monitoring and screen time and other features for parental control and havent thought about the age thing. So today when he turned 13, his age according to apple became 17 and we got some notification and it got us thinking that he will be allowed to use lot of age inappropriate content soon at next birthday and we wouldnt be able to do parental control. We are getting a bit worried since he will soon move to bigger school in city center and we dont want to loose parental control features.

We have already talked to our son about it and he has no problems with it.

So my question is how do I correct the age to 13 which he actually is? We have the passports of course to prove that if anyone from apple support would ask for it.

I see there are lot of post regarding problems changing childs age once account is created but not sure if we fall under those categories.

So is this change possible? Is it simply a matter of logging in to childs apple id account and changing DoB?