Family Sharing + Child accounts (Arcade/Music/TV)

We have an Apple One Family subscription (currently on the free trial).

Two adults and 3 children are all added and setup. As a Parent I have control over the child accounts etc. and e.g., 'Ask to buy' seems to be working fine for App Store requests. So the Family component seems to be working.

The subscription includes Arcade/Music/TV. These work fine for me and the other adult - e.g., their device (a new iPad) seems to have just recognised the subscription.

However, it is not working for the Children accounts. They should just be able to access the Arcade subscription.

They are on (new) iPads and instead the App Store keeps saying 'you can have 3 free months' etc.

Even if I try and do that and approve the subscription, it doesn't work. It goes all the way through, even prompts for iCloud credentials (for some reason) but then exits and nothing happens. The same is true f TV and Music - it prompts them to get new subscriptions rather than recognising the Family subscription.

I have verified as the Organiser that the Child has access to the subscription (i.e., in the Family section of my iCloud it says ... 'Subscriptions Child has access to...' and then lists Arcade (and TV / Music, etc.).

I had to manually share iCloud+ to share the storage space which has worked for the Child accounts to get access to the extra space.

It says that Arcade/Music/TV will be shared automatically (i.e., I cannot choose to not share it, for example.)

I have tried restarting the device, signed in and out of App Store on the Child iPad.

I feel like I'm missing something simple. Any ideas on how to get it working? I contacted Apple Support chat last night and I don't think they understood as they were focused on Purchase Sharing.