The Merced County Sheriff's Office and the Winton School District confirmed 34-year-old Edward Parsons was arrested on Thursday.
Parsons served as a student supervisor at the Sybil Crookham School in Winton.
Investigators say Parson allegedly sexually assaulted one 9-year-old girl and two 10-year-old girls.
The district said they learned of Parson's "inappropriate conduct after school" this past Wednesday. He was placed on administrative leave pending investigations.
Deputies say Parsons was booked into the Merced County Sheriff's Office Jail on three counts of felony lewd and lascivious acts on a child under 14.
Merced County Jail records show his bail was set at $450,000.
Detectives believe there could be additional victims and are urging anyone with information to contact the Sheriff's detectives.