DS rode the ride before seeing the movie. But he was pretty little at that point.
We did let him watch the movies VERY early, and it has worked out totally fine. PG-13 means Parental Guidance for those under 13, and that's exactly what DS got. There are still two scenes where he turns his back and we ff through it (rock/island prison scene in 2 and beginning of 3).
Anyway, through his 3 year, he wanted to watch the movie incessantly, but REFUSED to ride the ride. When he turned 4 he was ready for the ride again (we were at DL for his b'day) and it turned out that what bothered him about the ride was the Davey Jones screen. He thought it was really DJ and thought we were being eaten by him. I explained how the effect works, that it's not DJ, and worked out strategies to get past him.
Since your kids haven't seen the movies, they probably won't have the fear of DJ (by the way, DS isn't afraid of him at all in the movies, but the idea of being eaten by him was just too much) that a little one who has seen the movie would. He's just a weird tentacley dude (though with the way DS says it, substitute another word that is very similar to it for tentacles, LOL).
Peter Pan is a good one for getting a kiddo used to the idea of pirates BUT on the other hand, DS is more afraid of Captain Hook than he is of any pirate in POTC movies. Why? Because Hook is evil to the core AND is trying to kill CHILDREN. In the movies, the only children at obvious peril are at peril from the hands of the law-men. On our last visit to
Disneyland, a chance meeting with Peter Pan was almost ruined b/c PP was meeting people all while playing with a little mite of a girl who was dressed as PP...had her on the lookout for Hook...and my bigger boy was petrified in fear that Hook might come...had to do some quick thinking to salvage that chance meeting let me tell you!
Whereas he's had some of the best character interactions ever with Jack Sparrow, even before he saw the movies (knowing that cool JS was in those movies is what prompted his very long campaign of begging to see the movies), and we miss that character very much (he's gone from DL).
DS has never put a pretend dagger to anyone's throat, even when having us play with him (I'm the constant Elizabeth Swann and hubby is Will Turner). I'm not sure he's even thought to do it, but he knows there are rules even when playing as a pirate, and he knows very well that bad behaviour from any movie he watches will result in that movie being put away. Kung Fu Panda has been in time-out for a few days now b/c of that.
Anyway, I only ever recommend that parents try their best to figure out what movies are OK for their kids, have a screening of it BEFORE letting the kiddo watch it, and watch it with their kids many times, so that you can see what scenes might "get to" the kiddo so that you can FF through them, explain them, figure out what the problem is, etc. And so you know where possibly negative behaviour might be coming from if that happens. It's all about the Parental Guidance.
And as for the ride, I don't think it's necessary at all to have seen the movies in order to appreciate the ride. Though the ride might cause a kid to want to see the movie!