Why not to do 1:1 iPads

I had an interesting discussion last night with a friend about 1:1 iPad deployment in a primary school. She was horrified at the thought of every child getting an iPad which they could use all day long. She has an iPad at home that she lets her kids use, but she is always concerned to limit the amount of screen time her children are having, even if they are playing educational games. Life is bigger and wider than staring at and tapping on a glass screen all day. Maybe she has a point?