Jar Jar and the Ewoks were horrible. However, there was still plenty of violence in those movies. The violence was just presented less graphicaly. A movie can be dark and moving, while still getting a PG rating.
In episode one someone was cut in half (via special effects).
In episode two many winged humanoids were cut to pieces in close combat, and Skywalker had his arm cut off.
There was plenty of violence, just not lots of gore.
Violence seems to get movies a PG rating. Gore, vulgarity, or nudity appears to be what pushes movies to PG-13 or R. I haven't seen Episode 3 yet, but I wonder why they couldn't keep it PG.
Because the most important theme is Anakin's transformation into Darth Vader, both spiritually and physically. We need to know that once he decides to follow Palpatine he will willingly murder children, and we need to see the extent of his injuries in order for his cyborg body replacement to be understandable. RotS is not a happy fun movie like Episode I, and it's much better because of it.
My husband could not bear Jar Jar. He refused to see the movie until some friends invited us over for movie night - and guess what movie they had for us to watch - that Star Wars Movie with Jar Jar. So he had to see it. He got through it somehow.