Family sharing, ask to buy not working

Right, I've set up family sharing but all it has done is given the kids free rein to buy apps and music without password or permission on my account using their devices.

This mystical 'Ask to Buy' function appears to not exist.

Organiser account devices, all iOS 8.3

iphone 6

ipod 6

ipad mini 1

ipad air 1

KIds devices (logged into icloud etc with their own individual Apple id's)

5c, 8.3

5, 8.3

ipad 4, 8.3

So, I go: Settings > icloud > family sharing > tap the members names and all I can do is make them a guardian or remove them. Nothing about ask to join or anything else.

if I pick up my son's phine I can go to the App Store, pick a paid app, tap the price and it downloads it straight away, it doesn't ask for his password, my password, nor do I get a notification or any option to deny the purchase.

this could get expensive..... Or is that apple's plan???

ios 8 is still rubbish then, but is there a way to make this work myself, or should I just forget about it, like so many of the functions promised by Apple?

your help would be appreciate!