When the child began behaving abnormally, his 31-year-old mother took him to the hospital, where he tested positive for the drug, the Santa Cruz Sentinel reported Thursday.
It is presumed the boy ate the drug, but the mother proved drug-free and cooperative with authorities, police Capt. Steve Clark said.
Detectives are trying to interview the father to find out how the child got the drug. The father, who is estranged from the mother, stays in the home part of the time, the newspaper said.
"Any time you have a child who accesses illegal drugs in the home it's a gross case of irresponsible parenting," Clark said, while also acknowledging that removing a child from parental custody is a serious move.
No arrests have been made.