They had a day of family fun ahead of them.
Eric Moore, a father of three from LaPlace, Louisiana, was planning to take his kids out to eat before heading to the movie Angry Birds.
Before they left the house, police said, Moore jumped in the shower.
"The father said he was taking a shower when he heard a gunshot," Lieutenant Greg Baker of the St John the Baptist Parish Sheriff's Office told NBC affiliate WDSU. "He got out of the shower, and that's when he discovered that his daughter had accidentally shot herself."
Five-year-old Haley Moore had been playing with her father's handgun, police said. Moore told investigators that he had left his .45-caliber gun out on a table in the home, the station reported.
Baker told the station that the bullet entered Haley's right chest and exited under her left arm.
Joy Ursin, a next-door neighbour, described a harrowing scene outside the Moore home.
"The officer pulled up," Ursin told WDSU. "The kids ran out of the house screaming."
Ursin told the station that she took the children into her home and tried to comfort them while paramedics performed CPR on their sibling next door. As the incident unfolded, police tried to comfort the father, according to the Times-Picayune.
"The oldest kid, she repeatedly said, 'My sister shot herself. My sister shot herself. I don't know if she's going to be OK,'" Ursin told WDSU.
Moore was rushed to a hospital, where she died from her injuries, according to a statement posted on Facebook by the sheriff's office.
The statement confirmed that, according to detectives, the handgun had not been secured at the time.
"The first thing that goes through your mind is that it's a child and you want to do everything you can to help that child get through this ordeal," Baker told CBS affiliate WWL.
Ursin told WDSU that the children's parents are divorced and that they stay with their father every other weekend. She told the Times-Picayune that Moore is a responsible parent who took gun safety seriously. She told WDSU that Moore's children were "aware" of their father's guns but that anytime they were in his home, he put the firearms away.
She added that Haley was a "firecracker" who loved her father.
"All I can say is it's an unfortunate thing because Eric is a disabled military veteran and one thing is he has his guns, but he's not ignorant to the fact of the danger, especially when his kids are around," Ursin told the Times-Picayune.
"He would always stress how he had to secure [them], what he had to go through when the kids came," she added. "He made sure of that because he would get his kids every other weekend."
So far in 2016, at least 94 children younger than 18 have picked up a firearm and accidentally shot themselves or someone else, according to data from Everytown for Gun Safety, a gun-control group funded by former New York City Mayor Michael Bloomberg. The advocacy group, which compiles shooting data using news reports, found that 278 such shootings occurred in 2015.
In March, a Florida mother who bragged on Facebook that her 4-year-old son "gets jacked up to target shoot" was wounded when the child got his hands on a gun in the back seat of her vehicle and shot her in the back.
During one week in April, at least four children shot themselves with guns they found. A fifth child that week fatally shot his mother with a gun found in her car.
Moore's death is still under investigation, police said. Baker told WDSU that investigators want to know what caused bruising on the skin between Haley's thumb and finger. He noted that the discoloration could've been the result of the child's skin being pinched by the slide of the weapon after it was fired.
"Safety, everything is safety," Baker told the station. "If you're the owner of a weapon, buy a safe box, a gun safe. That's the way it is. Teach your kids. Teach your family about it."
Ursin said Haley's father was distraught. "We've spoken to him since. He's devastated," she said.