The party Saturday at Club Luis De Camoes was for Maria Depina, 22, of Brockton, who is eight months pregnant, the Boston Herald reported.
She said the trouble started when several party crashers "we didn't even know" showed up.
"My niece got shoved across the room. She's only 2 months old. A kid got hit in the head with a table. I was very scared. It's still a shock to me," Depina said.
The brawl did not end immediately when police arrived, Depina said.
"My brother got Tased right in front of me and a police officer pushed me on top of him," she claimed. "[The police] could have done a better job."
Stoughton police Executive Officer Robert Devine said Depina's allegations were "nonsense, absolute nonsense. They started fighting with each other. That's why we responded."
"The behavior was appalling. It was absolutely appalling. There's just no other way to put it," Devine said. "The worst part was there was a lot of children. Our officers were concerned about the safety of the little ones, while the people who were fighting apparently could have cared less. They were swinging chairs and smashing bottles."
In the end, Paulo Pires Depina, 24, Maria Depina's brother, Patrick Cardoso Lopes, 24, Aderito Lopes Deandrade, 22, and a 14-year-old boy whose name was not reported, were arrested on charges of disorderly conduct, resisting arrest and assault on a police officer.