It probably depends on the kid, but scary moments in otherwise lighter movies never bothered me and don’t seem to bother any kids I’ve known past or present. I would usually just hide my eyes during scenes I didn’t like, and I’ve seen my son and nephew and friends’ kids do the same. If they like the movie, they’re not gonna care. Kids just accept the fact that some things are scary, but again, everybody is different. It helps if the movie’s good, too!
I’ve watched the SW movies since before I can remember (born in '81 for those who care). The only thing that ever bothered me in the movies was Yoda’s death. Something about how the music changes right before he disappears and that nasty pillow left behind made me feel uncomfortable. Nothing in the SW movies bothered my son when he watched it at the age of four, and he found a lot of things scary at the time.
Old Star Trek reruns freaked me out way more than SW ever did.