The attacker then turned the weapon on himself and is in critical condition in hospital, police said in a statement.
According to an eyewitness, Several dozen children were in the building at the time of the incident and staff tried to hide them, and the fourth child is said to have suffered minor injuries.
Military police say they received several calls at 10:35 local time (13:35 GMT) from neighbors who reported that a man armed with a machete had entered the nursery and was attacking staff and children.
Police added that the man who has not been named first attacked a teacher who was at the entrance to the nursery and reportedly followed her into one of the rooms, where he also turned on the children.
“I heard screams [and] cries for help,” one employee who was near the nursery at the time of the attack, Aline Biazebetti, revealed
“I went outside and saw my colleagues calling for help: ‘Please, call the police, an armed guy came in and is killing the children.'”
Meanwhile, three days of mourning have been declared in Santa Catarina state.
This is not the first time such attacks happen however, there have been deadly attacks in schools before in Brazil, they have mainly targeted older pupils:
In 2011, 12 children were killed and 22 others were seriously injured when a 23-year-old former pupil opened fire in a school in Rio. The victims ranged in age between 12 and 14 years of age
In March 2019, two young gunmen killed five pupils, a school administrator, and a teacher at the Raul Brasil school near São Paulo.