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.
I did mention that I have not read it, and that it supposedly has a greatness that no movie has been able to capture. I am not likely to read it, but I accept that it may well be a great novel. Maybe it is an acquired taste. When I was in college, I did not care for the music of Gustav Mahler. My rrommate was constantly playing his symphonies, and I'd say "oh, no, not Mahler again! I hate that cacophany!" Now I play Mahler CDs all the time. Some people still think Mahler is a hack. From their P.O.V., that may be true.