Two students are thought to have been involved in the baking of the sandy-textured biscuits, which were sampled by at least nine youngsters at the Da Vinci Charter Academy just west of Sacramento.
Nobody has suffered any ill effects, and cremated human remains are not poisonous, although Davis Police lieutenant Paul Doroshov told The Sacramento Bee "there could be some emotional issues experienced".
One classmate, Andy Knox, told TV station KCRA: "I didn't believe her until she pulled out the urn. She told me there's a special ingredient in the cookie. I was kind of horrified."
Mr Doroshov added that the motives behind the culinary crime were unknown, but said the suspects were unlikely to be charged and that officers would leave it to the school to handle the issue.
He admitted he was unaware as to whether baking human remains into food could be considered an actual crime, noting that it would "probably take some legal debate to figure out".
In a letter sent to parents, headteacher Tyler Millsap said the pair were remorseful and that it had become a "personal family matter".
Source: sky news