No family notifications setup option 8.1.2

I've set-up family sharing to my sons iPhone 5 (his own apple ID) I have an iPhone 5C and an iPad 2 (organiser). When my son requests to buy an app, I get a banner notification on my iPad but nothing on my phone. If I go to settings / notifications on my iPad or iPhone there is no option to enable / modify family notifications hence I think it is just disable on my phone by default but there is nowhere on the UI where I can enable it. Any ideas would be appreciated