Two teenage brothers in Florida have been taken into custody after one of them allegedly shot and killed their older sister in an argument over Christmas presents, authorities said.

Pinellas County Sheriff Bob Gualtieri said in a news conference that the incident began Sunday afternoon while the two brothers were out Christmas shopping with their mother, older sister Abrielle Baldwin, 23, and their sister's two young children at a store in Largo, a city about 20 miles west of Tampa.

While in the store, the 15-year-old became jealous and accused his mother of buying more gifts for his 14-year-old brother.

"They had this family spat about who was getting what and what money was being spent on who," Gualtieri said Tuesday.

The family left the store and headed to their grandmother's house, where the grandmother was going to watch Baldwin's children – a 11-month-old boy and a 6-year-old boy – while she went to work. At the house, the argument continued.

At some point, the 14-year-old took out a handgun and threatened to shoot his older brother, the sheriff said. An uncle who was home at the time split the two boys up, and had the younger brother move out onto the driveway. Baldwin, who was carrying her 11-month-old baby in a carrier, went outside to speak with her brother.

"You all need to leave that stuff alone," she said to the 14-year-old. "Why you trying to start it? It's Christmas."

The teen "used some very very derogatory language" before he threatened to shoot her and "shoot the baby, too," Gualtieri said.

He then approached his sister and shot her in the chest with a semi-automatic handgun. Baldwin fell to the ground as did her baby, who was unharmed because he was in a carrier, the sheriff said.

Hearing the gunshot, the 15-year-old comes out of the house, said "you shot my ... sister" and then fired a handgun at his younger brother, striking him in the stomach.

The older brother threw the gun in a neighbor's backyard and fled to a relative's house, where he was later taken into custody by deputies. Because he made "self-harm statements," he was taken to a mental health facility, where he will be evaluated and then released to the Florida Department of Juvenile Justice, Gualtieri said.

Baldwin was taken to a nearby hospital, where she was pronounced dead on Christmas Eve. Her children will be placed in the care of her immediate family, Gualtieri said. Baldwin worked at a senior living facility.

The 14-year-old is in stable condition after undergoing surgery at a hospital for his gunshot wound. He will be released, like his brother, to the authorities. The state attorney's office will decide whether to charge him as an adult for the death of his sister.

"Now you've got a 11-month-old and a 6-year-old boy ... their mom is dead at the hands of a punk who was upset because he didn't get enough Christmas presents from his mom," Gualtieri said. "It's ridiculous."

The sheriff said multiple family members and nearby residents knew the teenagers "routinely carried guns." He expressed concern over the high number of stolen guns on the street, saying "This is the worst I've ever seen it." Most of the stolen guns, Gualtieri said, are either sold on the street or have been taken out of unlocked cars. The two teenage brothers were arrested in connection with numerous car burglaries in May, he said.