Johnny Lagunas, 20, of El Monte, worked at Garfield Elementary School.
The alleged crime happened in January or February, but it wasn't reported until recently.
Investigators say there could be more victims.
If you have any information regarding Lagunas, you're urged to contact the Alhambra Police Department at (626) 570-5159.
Lagunas is being held on $100,000 bail. He is scheduled to be arraigned this week.