I have heard people say that Lolita is a masterpiece of writing, and that none of the films do it justice. I have only seen the Kubrick film, and I do find the subject rather creepy as he presented it. James Mason was great in the film, but I do think Kubrick was doing a sort of nudge-nudge, wink-wink routine with the subject. As if to say to the audience, "admit it-you'd do her!" While I admire many of Kubrick's films, I have to say that Lolita is not one I care for at all. Maybe I cannot get past the subject matter.
Kubrick softened it a little by making Sue Lyon look rather "grown up". In films she made later, after she was an adult, she did not look much different that she did in Lolita. So in Kubrick's version, Humbert is attracted to a hot-looking nymphet who looks old enough to pass for adult. However in Nabokov's novel, Lolita was only 12 and not particularly attractive. Apparently it was the fact that she was a child that attracted Humbert, and that, IMO is just sick. There may be "art" in that book, but I fail to see it. Maybe I am not sophisticated enough.
Zefferelli's Romeo and Juliet is another matter. Apparently, a romance or marriage between people of that young an age was common dueing the Renaissance. As it is, Whiting was 17 or 18 when he played Romeo, and Olivia Hussey was 16 or 17, so they were either of the age of consent or near it (what is it 16 or 17?).
Not only were they shown in bed, there were flashes of nudity as well. Prude that I am, I believe the film could have done without the nudity. There is no doubt that in the "lark" scene as Shakespeare wrote it, Romeo is leaving Juliet's bed, so Zeferelli was correct in setting the scene there. There was simply no need to show bare breasts and buttocks in the scene IMO. The real star of R & J is the language, not actors' body parts. Remember that in Shakespeare's day, young boys played women's roles, so the plays about lovers were not structured so as to draw attention to the physicality of the actors, hence the reliance on poetic language to carry the passion of the story.
In any case, R & J is an inapproprate comparison (IMO) to a film about child rape. Lolita is a much better example though, and I must be too puritanical to see any artistic value in it (other than admiring specific performances, etc).
Have you read the novel? It starts when she's 12 and continues for 4 years. In 1961 there was no way to film anything like that. Kubrick later admitted that if had he known about the censor-related issues he would face he never would have attempted it. The novel is about a lot more then child abuse and is near the peak of American 20th century Art in general.