“At the moment, it’s being treated as murder with an alternative charge of manslaughter,” police spokesperson Lars Liewenborg told the TT news agency.
Police don’t know for sure what sort of weapon was used and are currently looking for witnesses.
“There were people in the area, but we don’t know if there were any witnesses to the actual event. There might be someone who saw something afterward,” said Liewenborg.
Södermanland County police received a call about the find around 11am on Thursday.
When they arrived at the address, located in the Arnö suburb of Nyköping, about 100 kilometres south of Stockholm, they found a dead child and a woman with severe knife wounds.
Police have yet to arrest anyone for the suspected murder and attempted murder, but say they are getting a better understanding of what happened.
“We know more or less what has happened, but we’re not going out with that,” said Liewenborg.
According to police, the 30-year-old woman has been taken to hospital to have her injuries treated.
The call prompted a large police and emergency services response but police have yet to release any details about the child’s age or other information about the case.
“It’s too early to say. I don’t want to release that before I’ve spoken with a prosecutor,” Liewenborg told the local Södermanlands Nyheter newspaper.
He added that there is no reason for other residents in the area to be concerned about additional violence.
“This is within a small group of people, it’s within a family, so there is no need to worry,” he said to TT.
According to police, other family members were home when the woman and baby were injured.