The crash was reported around 4:40 p.m. local time at La Petite Academy in Saugus, a neighborhood of Santa Clarita, according to the Los Angeles County Fire Department.
The injured kids had to be airlifted to a local trauma center, fire officials said. There was no immediate word on their conditions.
Chopper footage from local outlet KTTV showed debris around a smashed front window at the one-story building that houses La Petite, a national chain that offers daycare, pre-school and kindergarten.
The incident remains under investigation.