As far as I'm concerned... The transporter malfunction in ST:TMP is good clean fun for kids of all ages when compared to the sound of Maximillian's rotating claws drilling into the chest of Tony Perkins, in "The Black Hole", which came out the same year, was also G-rated, and was a freakin' Disney film to boot!
Plus, you can never tell what will freak kids out at what age. My little sister sat through the original "Star Wars" without a peep, Darth Vader and all, but was so terrified by the scary lady in "The Rescuers" that we had to leave the theater . . . .