Branden Christian died after he was critically injured in a shooting on Hays Drive, where police said Allen D. Cashe opened fire on Tuesday.
Branden's 7-year-old brother Brendon Christian and their grandfather 56-year-old Bertis Gerard Herring Jr. were also injured in the shooting at the home.
His mother, LaTina Herring, 35, died in the shooting.
Sanford police said the incident was reported around 6:20 a.m. at Hays Drive and West 24th Street.
Officials said 7-year-old Brendon remains in critical condition at Arnold Palmer Hospital for Children in Orlando.
Bertis Gerard Herring Jr. also remains in critical condition, officials said.
“It is heartbreaking to know that this young child lost his life needlessly, and in such a violent manner. Our
hearts and prayers are with his family during this tragedy. We will continue to focus on the case against Allen Cashe and to seek justice for all of the victims and their families," Sanford Police Chief Cecil E. Smith said on Tuesday.
The Seminole County Schools superintendent also offered his condolences to the family on Tuesday, and said grief counselors will be available.
"We are deeply saddened to learn that one of the young student victims of yesterday's horrific and senseless shooting has passed away from his wounds. The entire Seminole County Public Schools district grieves for the family and entire Sanford community. There are no words to describe the tragic loss of a young and innocent life taken so soon. We have placed grief counselors at all our schools directly impacted by this incident for any student, faculty or staff member that requires their services to cope and heal. The counselors will remain in place for as long as necessary," Walt Griffin, superintendent, Seminole County Public Schools said.
Two innocent bystanders, Lazaro Paredesquelite, 43, and Winter Springs High School student Rakeya Jackson, 18, were also shot by Cashe after the shooting in the home. Both are in stable condition, police said.
Police are calling both shootings "horrific."
The shootings happened hours after two incidents involving Cashe and Herring, who were in a relationship, police said.
Officers responded to the Wawa gas station at 3:20 a.m. on Monday morning in Sanford, where the two were having an argument over keys.
Sanford Police Chief Cecil E. Smith said Cashe was searched and, at the time, had no weapons on him, nor in his vehicle.
The pair told officers that the argument was not physical, and officers separated and calmed the pair down.
Seventeen minutes later, police received another 911 call from a caller saying a woman was being battered while walking down West 25th Street.
While trying to find the alleged victim, later identified as Herring, police received another 911 call saying that the man had a gun, according to a news release.
Police identified that Cashe and Herring were involved in this second dispute, and they found the pair having another argument about keys.
Police said that Cashe did not have any weapons on him at the time. Herring gave police a bag of Cashe's belongings, which included a 9 mm Glock handgun, Smith said.
Officials said the 9mm Glock was not used in the shootings, and at no time did Cashe possess or handle it.
Officials said Cashe was not arrested because the disputes were civil and police had no evidence that any crime had taken place. Smith supported his officers' actions.
Three hours later, police said Cashe returned with an AK-47 and shot Herring, her two sons, and their grandfather.
Cashe was arrested in connection with the shootings and he is charged with first-degree homicide, four counts of attempted first-degree premeditated homicide, one count of second-degree attempted homicide, one count of felon with a firearm, and one count of violation of parole -- felon with a firearm.
Cashe is expected to appear in court on Tuesday at 1:30 p.m.