James Jensen was taken into custody Friday after police conducted a complete interview with the child and obtained a warrant for his arrest.
Jensen was located at his home and arrested without incident.
The mother had contacted police on Monday after being concerned about the peculiar behavior of her daughter. When the mother asked if anything had happened to her, the daughter revealed something had occurred at the day care provider's home, police said.
At this time, only the one victim has notified authorities, but based on the investigation, Martinez police that there may be additional victims who have not yet come forward.
The state's Community Care Licensing agency has also been notified because Jensen was a state licensed day care provider, according to police.
The investigation is ongoing, and anyone with information about the case is asked to contact Detective Mike Estanol at (925) 372-3452.