In order for underaged children to travel/return overseas unaccompanied of accompanied by only one parent, you will need a document called “autorização de viagem para menores” (two copies) or autorização judicial (issued by the Vara da Infância e da Juventude or the Vara de Família). These documents are presented to the Federal Police (Marshal) agent at the airport, port or borders at the moment of departure/exit of Brazilian territory. One of the copies will be kept by the officer and the other will remain with the minor or guardian. These authorizations do not need MRE (Ministerio de Relações Exteriores) legalization (see Legalizing documents post) or Consulate/Embassy legalization of the destination country unless they will subsequently be presented to the authorities of the country. In this case, the document must be signed by a notary public recognized by the MRE and then sent to the MRE or destination country consulate/embassy.
The MRE does not recommend third-party services.