The two attempted heists in the state of Ceara began around 2:30 a.m. in the downtown area of the city of Milagres.
Robbers at one bank took several people hostages when police surrounded the area, according to a police statement. A firefight broke out, leaving several dead. Authorities have yet to identify the dead.
Two suspects were apprehended, according to police.
Milagres Mayor Lielson Macedo Landim told local media that two children, between 10 and 13 years old, were killed in the shooting. It was not immediately clear how the hostages were taken. Police did not immediately respond to email and phone requests for more information.
Latin America's largest nation routinely is the world leader in total annual homicides. Ceara is one of the country's most violent states.