Police suspected the 59-year-old woman had "restricted her children's freedom... For quite a few years," spokeswoman Ewa-Gun Westford told AFP.
According to tabloid Expressen, one of the now adult children managed to briefly leave the apartment and convince a neighbour to call the police, saying that they had been locked up for over a decade.
"The blinds were always pulled down there and we haven't heard any noise from the apartment," a neighbour told the paper.
Investigators were questioning the woman and the children -- all aged over 18 -- at a police station in the southern town of Kristianstad.