My own kids are 5 and 3. I am acutely aware that this problem is looming for us. So far, my kids almost never play with our iPhones beyond FaceTiming grandparents; they get access to an iPad on the one international flight we do a year; and TV is a rare, weekly treat. Both of us work so this is tough to enforce, but I've already fired one nanny in part over it. I am hoping that their own imaginations will become more appealing places to play than some screen, but I recognize the forces I'm fighting against.
We're not luddites at all; they understand that music and fun things come from the internet, they get that there are fun apps on the phone they can occasionally play, we don't make any secret of our own use of technology, but we position it as a grown-up thing, like beer or going to bed after dark in the summer.
I don't really see how our approach can survive first contact with grade school.