Authorities in the western Mexican state of Michoacan discovered the bodies, believed to be officers who had gone missing a week ago.
The boy was taken to a children's hospital in critical condition.
"They are suspected in a number of troubling incidents in Queens in the last year or two."
Charles Frederick Landeros, 30, was killed following a custodial dispute on January 11.
The names of three of the victims were withheld to respect their family member's wishes.
"We will be looking for you, and we will find you," said Sheriff Jesse Razo, who urged the suspected shooter to turn himself in.
The girl's mother and 7-year-old brother were killed by her father in a domestic dispute on December 16.
The 12-year-old boy accidentally shot his younger sister in the head while their 16-year-old sister babysat them.
Detroit police said they would not pursue charges against the woman, saying she acted in self-defense.
Bradford was shot in the back of the right side of his head, in the neck and in the right side of his back.
A gunman pulled up alongside a car on I-75 in Toledo, Ohio, and opened fire, hitting one of the three children sitting in the back.
"In the city in which I live, I hear and see examples of chaos almost everyday," Parks wrote. "Little children are victims of senseless gun violence."
The four victims included two men and two women, ranging in age from 20 to about 40, police said.
An animal rescue organization is offering a $5,000 reward for information.
Sheriff Larry Fowler said the deputy was hit in the leg and taken to hospital, where he is expected to make a recovery.
Officials said that a bus driver pulled up to the home where the shooting occurred and rendered aid to at least one victim.