Protect children? Protect children from what?
The question presupposes that there is something about pornography that would be harmful to children. The very fact that no-one has questioned the premise of the thread title could be construed as symptomatic of a sexual psychopathology -- caused,in part, by a lack of exposure to sex and nudity (ie: pornography) as children.
Perhaps pornography is good for children, and should be encouraged.
Consider:
In many tribal cultures nudity and sexuality is treated casually and matter-of-factly. In these societies you won't find damaged children. If you distributed a handful of Playboy magazines to a group of adolescent boys they actually would "just read the articles."
In the Netherlands any child can buy a pornographic magazine. They're right there on the rack with the newsmagazines.
I never noticed that the Dutch were any more depraved or warped than anyone else.
The fact that we find pornography salacious and titillating is not a Natural reaction. It is a warped reaction caused by our parents "protecting" us from it as children, thereby unwittingly transforming it into something fascinating and forbidden.
Our titillation with sex and nudity is artificial and entirely cultural. What our great grandparents' considered salacious, a bare leg, for example, wouldn't raise an eyebrow today. Yet I'll bet grandpap would have been quick to slap his hand over little Johnnie's eyes -- to "protect" him -- had a fall or errant breeze exposed a bit of feminine leg down on Main St.
Have you ever been to Hawaii? Were you greeted at the airport by a colorfully dressed native lady draping a lei over your head?
If you'd chosen the island of Yap for your South-Sea vacation you'd also have been leid (?) by a native lady at the airport -- but she would have been topless. Toplessness is normal on Yap. But, as the tourist brochures warn, don't even think of wearing shorts there. Bare your thighs in public and the shocked citizens of Yap will quickly usher their kids indoors, to "protect" them from this gross indecency. Some might even pull out their cell-phones to report this public lewdness the authorities.
Sunstone's question, of course, hinges on how one defines pornography.
I would certainly want to restrict any exploitative pornography -- or any exploitative non-pornographic activity, for that matter. And there is evidence that scenes of violence, anger and abuse actually can be intrinsically harmful -- unlike nudity and sex, yet there is little pressure to shield these from callow eyes.