The guard sprayed them with alcohol before setting them on fire, according to one news account.
The guard also died in the incident.
Four children and a teacher died and several others were injured at a day-care center in eastern Brazil on Thursday when a guard doused the school with alcohol and set it alight, officials said. "We believe a security guard at the nursery set himself on fire and set fire to children in the kindergarten".
Janauba's mayor decreed seven days of mourning. With only 2 hospitals in the small town of 80,000 people, numerous more seriously hurt were taken by police helicopter to Minas Gerais' capital Belo Horizonte, more than 500 kilometers away.
About 50 people were hospitalised with injuries, said Bruno Ataide Santos, director of the local hospital.
Reports revealed the security guard, identified as Damiao Soares dos Santos, 50, was mentally ill and had worked in the centre since 2008.
"I woke up early to drop him at the nursery", Jane Kelly da Silva Soares told the local O Globo newspaper. State police said officers were visiting the suspect's family members to try and determine the motive behind the attack.
"This could have been worse because the babies' room was in the hall next door. I want to express my solidarity with the families".
"I am very sorry for tragedy that led to death of 4 children in Janabua", said Brazilian president Michel Temer, social media. I, who am a father, imagine that this must be a most painful loss.