An RCMP spokesman confirms in an email that the person is under 12, but that further details won't be available until a news conference on Tuesday.
Lee Bonneau was found fatally injured on the Kahkewistahaw First Nation last Wednesday.
He died in hospital from his wounds, which RCMP say were consistent with an assault.
Lee was last seen playing outside the community's recreation centre while his foster mother was inside playing bingo.
RCMP say the chief of the community, Sheldon Taypotat, will be at the news conference along with officials from the province's justice ministry and family services department.