Sky High (2005 movie)
His parents go to the prom instead.  There was going to be a ceremony to honor the best superhero of all time.  During the prom, however, it is revealed that Gwen is really a villain named Royal Pain.  The Commander thought he killed her off, but when he zapped her, she simply became a baby instead.  The years passed and she grew into another teenager.  Royal Pain puts on her suit and uses her weapon to make everyone become babies.