I get asked (as I assume a lot of people here do) for advice about buying computers. If they have kids I always say ' Don't let and under 16 year old have unsupervised access to the internet'. Get a nice family computer in the living room or kitchen until then, get several if you like but don't let them hide in their bedrooms. As a parent you don't have to oversee everything they do just being around is enough to keep a lid on the worst excesses.
None of them ever take my advice.