Isn't this just telling parents that the internet will suddenly be safe, a government sanctioned message to that effect is quite a bit stronger than your ISPs salesperson. Of course, the filter will either resemble China or have holes so assuming the latter any responsible parent will still want to monitor their children's usage.
The effect of this law seems to be constrained to making David Cameron (and other not-very-technically-knowledgeable parents) feel that he's a responsible parent, but to be honest I'd rather taxpayers pay for a nanny for him than for this ridiculous law - cheaper and much more effective.