I created a Family Sharing invitation and sent it to an email address. In a new iPad mini (running iOS 8.1.2) I find the email message and click on the "View Invitation" link. It immediately takes me to the iCloud settings, but there are no details about the invitation and no indication about how I should proceed. This iPad has not been previously associated with any Apple ID. How can I associate this device with the Apple ID associated with the invitation?
Confirm that your device is running the version of iOS that you think that it is under Settings > General
It might help to associate devices with that Apple ID, or at least log in to iTunes with the Apple ID to make sure that everything about the Apple ID works http://support.apple.com/en-us/HT204074
You can also get to the invitation from Settings > iCloud > Family Sharing
here is info from the start http://www.iphonehacks.com/2014/09/setup-family-sharing-iphone-ipad-ios-8.html
I was able to resolve all of my issues.