According to Brazilian news site G1, a protest took place at the opening ceremony, but the TV cameras ignored it.
The site reports that Werá Jeguaka Mirim was one of three children who released white doves just before the kick-off of the first game, between Brazil and Croatia.
As he left the field, he opened a banner calling for new boundaries for Brazil's indigenous lands. Pictures of the boy's protest were posted on the Comissão Guarani Yvyrupa (CGY) Facebook page.
Earlier this month Guarani Indians used their bows and arrows to stop drivers from passing a roadblock they imposed in front of the Sao Paulo State legislature.
A status update on the CGY's Facebook page says: "Shame that the mainstream media has diverted the cameras and chose not to broadcast the only true message of this ceremony."
Werá apparently hid the banner inside the pocket of his white uniform. His father, a writer, told the site he was surprised by the gesture: "I myself did not know he was going to [do that]. He is calm, quiet, not shy."
He said that some people on Facebook were critical when they found out his son was attending the event, but that his son has now received dozens of friend requests.
He added: "We are not against the World Cup, we are against the injustices that cause the demarcations, which is the main cause that we have been fighting for years."
The image is beginning to go viral and is being shared along with links to this feature on the Guarani in Sao Paolo.