"We're not against children taking part in Carnival, but we're against them in that position, which promotes a sexual image of children and teenagers," said Carlos Nicodemus, the president of the Council for the Defense of the Rights of the Child, in Epoca magazine on Sunday.
"The position has a high sexual connotation," Nicodemus said.
The council has sought to legally block the child from taking on the role.
The samba school, meanwhile, underlined that Lira would not be dressed in provocative clothes.
"It was a great choice and perfect to place a sweet, pure and delicate girl in the same position as that which was held by Luma de Oliveira and Juliana Paes (Brazilian sex symbols)," scenographer Edson Pereira said on the school's website.
Lira's parents told Epoca that their daughter, who started dancing aged two, was born for Carnival and samba.
Festivities this year run from February 12-17.
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