All our 4 little ones have iPads and have done so from about 18 months.
They are never unsupervised , its really that simple. I see huge value in online learning and some of the educational apps available are outstanding. They practice their reading , they write stories and become familiar with technology and the gain the ability to source answers to their questions.
Having said all that , when they come to us, they bring their iPads for a quiet half hour while tea is being prepared but the rest of the time, we play games, go outside and get dirty , we talk, sing , paint the list is endless because what they cannot get from iPads are the nuances of conversation.
They cant see and become able to work out human interaction, body language , tone and content.
I have never had to threaten to take away their devices , I simply say No. My house my rules and they know that. Arguing with Nana is a pointless activity and wastes time that can be used on far more fun things.
Smashing their iPads is probably the most ridiculous thing I have ever heard and simply indicates to me that anyone who does that has a) more money than sense and b) is in need of some publicity :-) !! Its not what normal people do .