Setting up an apple id for a child over 13 but under 18 yrs

Quick update - my son's Mac has the Finder>Pictures>Photo Library! It's just disappeared from my Mac and I believe it's an iCloud issue. Nevertheless, this means we can use his Mac to transfer the library to an external hard drive! It's a solution and then I won't rely on iCloud again.

Thank you Eric for your reply but unfortunately this is exactly what I've already done and said so in my comment. I used Family Sharing to invite him and it failed multiple times and that is why I tried to set him up with an Apple ID which also failed because of the age range and even though he's still a minor I can't create an adult account either. It's a vicious loop. This video is useless because it's just childish animations and doesn't show steps on your device to follow eg click on here and enter this information etc. From the comments on the video I'm not the only one frustrated and infuriated over this iCloud Family Sharing process.

So, Eric it seems that after all the inviting, logging in and out of iCloud etc yesterday something finally kicked in and my son's mac has synced with notes and photos BUT now I go into iCloud drive and I have an empty Downloads file, Previews are his not mine, Desktop is his not mine... all my stuff has gone and I can only view his and there's NO PHOTOS FOLDER. I wanted to rescue my Photos but all instructions online claim the Photos Library is by default in the Pictures Folder under Finder - not true - it shows 102 photos over 8 yrs instead of 6,262 items. I desperately want to back my precious items up because everything is going haywire.

Why can't I access my photos in Finder > Pictures if it's the only source to use? Why has all my iCloud Drive items disappeared and only my son's visible? Why aren't my photos in iCloud? I decided not to keep stressing over a separate Apple ID since his mac was syncing but more problems have emerged. What's going on? I was trusting in iCloud to be storing everything as my backup other than Time Machine because it doesn't do photos.

Thank you again Eric for your patient response. Because all the online instructions for backing up Photos to an external drive say go to Finder>Pictures and your Photo Library will be there by Default. It's not, there are only 102 photos and when I type in the search bar Photo Library it comes back with No Results. I have looked in Time Machine and it backs up my Pictures Folder BUT that's the one that doesn't have my photo library so NO PHOTOS BACKUP!

Clearly if Time Machine backs up your photos it's because your photos are in Pictures, apparently where they're meant to be.

Time Machine has all my docs and downloads but iCloud Drive doesn't but at iCloud.com my photo library, documents (only between 2020-present though), downloads and desktop are there BUT Preview folder only shows my son's stuff and in Advanced settings asking to Restore Files the circle spins awhile and then says it can't do it.

So, it looks like there's definitely something awry regarding Photos, despite the fact that when I do a search and select 'Show in Finder' I'm told the pathway is (name)>Pictures>Photo Library - ????

All I want to do now is find a way to backup my photos because I don't trust what iCloud is doing and it appears I'm going to have to manually select items and copy to an external drive OMG I have 6200+ photos.

At least my son's Mac is being backed up by iCloud and he now can see notes, docs and photos.

For some reason though Notes is not in iCloud Drive or at iCloud.com or in Time Machine - is this normal? Because I have put a lot of important stuff in there believing it was being backed up.

OK, so I need to work out how to manually back up my Photo Library and apparently Notes too... at least I can give up on the grief of trying to give him an Apple ID - I can't believe how many online sources, including Apple, say you must have the same Apple ID across devices for syncing and sharing to work and just as many saying DON'T share Apple ID's, it's no wonder this becomes hair-pulling scenarios.

Again, I appreciate you trying to help.