The victims were members of a baseball team and their families, Juarez Noticias reported Monday.
A trophy was found in a courtyard of a home in the city of Loma Blanca where the attack occurred just before 10 p.m. Sunday.
Police said that in addition to the child, seven men and two women were killed. Another person was injured.
Loma Blanca is about 60 miles west of the capital Mexico City.
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