Shared photo streams on/off switch not visible
Just trying to set up Shared Phot Streams on my iPad and my parents.
Got as far as setting one up on ours, and the email has arrived OK on my parents, with a link to Join this Photo Stream.
When I click on the link, I get a prompt to Join this Photo Stream, and a message saying that Shared Photo Streams needs to be switched on.
But in the settings the option to turn on Shared Photo Streams (that I can see on our iPad) is not there, so I can't turn it on.
As far as I know iCloud is all set up, as I've got Messages and FaceTime all working.
Any help with what I might be missing would be greatly appreciated.
Thank you!