Xbox Live Gold Account, my son can't use it?

So I bought an x-box for my son a couple years ago (he's now 11). I have him setup as a child on my box and have removed content restrictions.

However, he can't access Xbox live Gold. E.g., he can't play Fortnite for instance or any game that requires Xbox Live Gold access.

I only bought it for him and had set myself up originally as the parent to be able to simply lock him out from purchasing stuff. Is there a setting I'm missing somewhere that should allow this as all articles I've read seem to indicate he should be able to access my Gold account??

You will need to set up the Xbox One as your home console. This has likely been done by default, but it can't hurt to check. Here is the official guide on how to accomplish this: Set up home Xbox.

This should be enough to allow your child account to access Gold. If not, be sure to check in the settings if you haven't selected a restriction level that doesn't allow your child to play online.