This is the 2318th most frequent Portuguese word.
infantil
"Infantil" means "childish" or "related to children."
Here, 'infantil' is used as an adjective to describe the type of book being aimed towards children (children's book).
Ela comprou um livro infantil para seu sobrinho.
She bought a children's book for her nephew.
In this case, 'infantil' is describing the behavior, implying it is immature or typical of a child.
O comportamento dele foi considerado infantil pela professora.
His behavior was considered childish by the teacher.
Here, 'infantil' characterizes a section within a library, indicating that it is designated for children.