Another 40 people were injured in the attack in the city of Janauba, Xinhua news agency reported.
According to mayor and police, a security guard at the school doused the children in alcohol and then set them alight.
The regional hospital of Janauba reported that 40 other people were brought in, 25 of them with burns and 15 in a state of shock. The latter have since been released.
Among the patients remaining in hospital, 14 were children aged four and five, and the remainder are kindergarten staff. All of them present burns on over 20 per cent of their bodies.
The attacker, aged 50, had worked as a night watchman at the school since 2008 and allegedly suffered from depression.
President Michel Temer reacted to the horrific incident, posting on Twitter: “I immensely regret this tragedy involving children in Janauba. I want to express my solidarity with the families.”