"She had no explanation. She had drunk alcohol and smoked cannabis," prosecutor Klas Norelius said.
The mother, whose name was not reported, confessed in a Malmo court to reckless behavior, bootlegging and narcotics crimes for the incident, The Local reported Monday.
At the party, which happened in June, the 3-year-old was filmed as his mother urges him to smoke a cigarette.
"Take a toke then you little … inhale then … come on now. Inhale a little. Light it up now, for goodness sake, get the damned thing going," the mother is heard saying in the video.
The fact that the incident was caught on camera meant the prosecution had a strong case against the woman, Norelius said.
Defense lawyers for the woman argued some parents allow their children to try alcohol and cigarettes.
"He will have to speak for himself, but in my opinion you should never offer alcohol to a 3-year-old," Norelius said.
The prosecution is hoping the woman will be fined.