Of course, this is just a guess-
But, underneath it all is a question: how is this effecting their brains and mental development?
I have three children of my own, and I worry even though I do allow them access to the internet, part for school and, in small doses, games & entertainment. There is a time limit set with a timer, because they will play for hours if permitted.
The internet is powerful, so much so that it can drown out the real world. Like all addictions, there is a 'man takes a drink, then a drink takes a drink, then the drink takes the man' effect. The neurochemical rewards computer games offer a young mind seeking stimulation are undeniable.
It is a constant battle to keep my children focused on the material of the internet rather than the experience of it as an end game. I am hoping they learn to use it to accomplish tasks away from it, rather than seeing their self-worth and sense of accomplishment as tied up with the internet.
So far, this seems to be happening. Crafting projects, books, and conversations with live people still seem to be pretty important around here, but it is because of self-discipline above all else.
Still I worry that perhaps I am laying the groundwork for later problems. I wrestle with the possibility that the one-hour allotment is still too much. What I have come to accept at some level is that the internet will be with them long after they are emancipated by age, and so I must show them the way of moderation... and then pray.
The internet is a dangerous companion. In some ways, it is like being a lion-tamer: while it may serve your purposes and be 'obedient,' there is still a wild animal in front of you that can revert to a very dangerous beast at the drop of a hat.
Susceptibility is the key: am I, or my children, healthy enough to use it? If not, then we are susceptible to abuse not only the internet, but any other manner of substance or behavior that releases similar biochemical.
In the end, the 'net is neutral: we are the problem.