The suspect also set himself on fire and was taken to hospital with burns covering nearly all his body after the attack at Innocent Children's People Municipal Education Centre in Janaúba, in Minas Gerias, south east Brazil.
The guard, who was aged about 50 and identified as Damiao Soares, died in hospital several hours after the incident, which left him with burns all over his body, Santos told AFP.
At least five toddlers and six teachers have died during a horrific arson attack at their nursery this morning.
The children who died ranged in age between 4 and 6, CNN reported.
Two girls and four boys, all aged four, were killed and dozens of people were taken to hospital with severe burns in Janaúba, southeastern Brazil.
Governor Pimentel ordered the creation of a special operation to receive the victims, both in hospitals in the region and in in Belo Horizonte.More news: Andres Iniesta signs new lifetime contract with Barcelona
The attack on the day care facility Gente Inocente (literally "Innocent People", in English) shocked the town of 72,000 in the countryside of Minas Gerais.
The daycare centre in Janauba, in the state of Minas Gerais, cares for about 70 children, according to local media.
Investigators are still trying to determine a motive for the brutal attack. "I want to express my solidarity with families", wrote Brazilian president Michel Temer on Twitter.
He allegedly came to the center Thursday to turn in paperwork before starting the blaze.
Janauba's mayor decreed seven days of mourning.