my Whatsapp icon has disappeared and i cant download it as it says open in App store! please help!!

So, now the problem is solved....

Whatsapp changed with there update in February the the allowed age to 12+ and the restrictions are for my daughter at 9+ let disappear the icon ..

Change the restrictions to 12+ and the icon is back ;-)

i have outsourced whatsapp (menu settings/general/memory) then the icon is back on the home menu, so I can download the app, but at 100% the app-icon is hidden and in app-store iOS tells me that the app is installed but pressing "open" does not work; so I need help too. iOS 11.2.6 is installed.