By Vanessa Buschschlüter
Another four children were injured by the 25-year-old man who entered the creche at around 09:00 local time (12:00 GMT) on Wednesday.
At least one of them is reportedly in a serious condition.
Police told local media that the attacker had surrendered and was in police custody.
In a statement, military police said that the assailant had handed himself in at one of their stations in the town.
Firefighters said three boys and a girl were killed in the playground. They are thought to have been between four and seven years old.
In total, around 40 children had been inside the Cantinho Bom Pastor nursery – which translates as Good Shepherd – at the time of the attack.
They added that the assailant had jumped over a wall in order to gain entrance to the privately run kindergarten and had apparently targeted the victims at random.
A teacher, Simone Aparecida Camargo, said it was “a scene that you’d never imagine you’d see in your life”.
“A colleague came running saying ‘close the door, close the window, because someone is breaking into the building. At first we thought it was a robbery because he tried to break in, so I locked the babies in the bathroom, then someone came to the door saying ‘he’s come to kill’.”
She said the entire preschool class had been in the playground.
Ms Camargo added that as well as a hatchet, the man also carried other weapons, although she did not specify what these were.
Parents ran to the kindergarten as news of the incident spread.
City officials have suspended classes in Blumenau until at least tomorrow.
The governor of Santa Catarina state – where Blumenau is located – has declared three days of mourning.
It is not the first time a kindergarten in the state has been the target of an attack. In 2021, an 18-year-old man killed two staff members and three toddlers in a creche in the municipality of Saudades.
The incident also comes just 10 days after a teenager stabbed a teacher to death and injured another four people at a school in São Paulo.
President Luiz Inácio Lula da Silva tweeted that “there is no greater pain than that of a family that loses its children or grandchildren, even more so when it’s through an act of violence against innocent children who can’t defend themselves”.
The city has about 360,000 inhabitants and is a popular destination with visitors exploring the German heritage of the region.
