The thing that disturbs me about this argument is that IMHO it's a slippery slope towards "back in my day, we didn't have this new-fangled stuff". We have to be extremely careful that our arguments have more substance than that. That requires a lot of introspection, to be honest.
See, my grandparents worried that the new technology that my parents grew up with would somehow make them dumber (growing up with radio, parents getting television); my parents' generation worried that the technology we grew up with would be bad for us (too much computer, too much gaming, too much Internet). The upcoming generation of parents will grow up wondering whether VR and AR is going to ruin their kids' chances.
Yet kids ALWAYS adapt. They don't view smartphones or tablets as anything particularly out of the ordinary. It's just their ordinary. I'm certain their brains will build on top of this foundation. That's the thing - brains are extremely adaptable. All of us adapted.
There's a term for this worry - it's called 'Juvenoia':
https://www.youtube.com/watch?v=LD0x7ho_IYc
http://time.com/19818/whats-really-wrong-with-young-people-t...
Now, I'm not saying that this is a discussion that shouldn't be had - it certainly should. I just think we all need to be mindful about where our concerns might be coming from.