The five year-old boy died overnight, the hospital treating him said in a statement.
The total toll from Thursday's blaze is now 11: nine children, the teacher who died trying to save pupils, and the security guard. About 40 people were injured and 19 were still in hospital, including three in a serious condition.
On Sunday, Brazilian President Michel Temer posthumously decorated the 43-year-old teacher, Heley de Abreu Silva Batista, for her bravery during the fire at the nursery school in Janauba, a small town about 370 miles (600 km) from the state capital of Minas Gerais.