A girl of 10 who complained at school of stomach ache gave birth just hours later.
She was rushed to hospital by teachers and found to be in the late stages of labour.
Although only seven months pregnant, the girl gave birth normally.
She told police her stepfather, 40, abused her.
He is now accused of rape.
The girl’s mother claimed she had not seen her daughter’s stomach bulge and she had no idea she was pregnant.
According to police, the girl’s mother said that her daughter started to struggle at school and become more introverted from October last year.
Police in Belo Horizonte, south-east Brazil, said: “The mother alleges she and other family hadn’t noticed.”