The child was proudly displaying packets of a powdery substance to his kindergarten classmates in Bridgeport, Connecticut, on Monday when his teacher noticed what he was holding, Detective Keith Bryant of the Bridgeport Police Department said.
"He was waving it around," Bryant said, adding that the teacher collected the packets and immediately notified her supervisors.
Authorities were called and a field test determined the substance was heroin, he said. Later, the child's stepfather, Santos Roman, 35, showed up at the school and was arrested.
"He went to retrieve it (the heroin), and it wasn't there so he came back for his stepson," Bryant said.
Roman was arraigned on Tuesday on three drug-possession charges, including intent to sell within 1,500 feet (457 meters) of a school and risk of injury to a minor, police said. Roman was held on $100,000 bail.