The security spokesman for Nuevo Leon state says a 5-year-old boy, a 7-year-old girl and 40-year-old man died, while three more adults were wounded.
Spokesman Aldo Fasci says the attack occurred on Saturday at a home in Santa Catarina, a suburb of the northern city of Monterrey.
Authorities say a relative of the home's residents had recently been in prison on drug charges.
The state offered a reward of just under $50,000 for information leading to the arrest of two suspects identified in the attack.