(CNN) The fatal shootings of two children, 8 and 15, over the weekend in St. Louis were the latest casualties in what has been a deadly summer for young people, police said.

At least a dozen children 16 years old or younger have been fatally shot since April, police said.

Local reports indicate a 10-year-old girl was among the victims in a triple homicide over the weekend , but it wasn't immediately clear if she was shot or stabbed. The St. Louis Metropolitan Police Department did not include her in a list of young gunshot victims.

On Saturday, officials announced its grim formula for calculating rewards leading to the children's killers: $25,000 for each child younger than 10, for a total of $100,000.

But the reward money will expire Sunday, city officials said.

"The message to the shooters is now there will be a significant incentive for anyone with information that could lead to your arrest," Mayor Lyda Krewson told reporters at a news conference, according to CNN affiliate KPLR.

The St. Louis Metropolitan Police Department said it is investigating nine of juveniles' deaths as homicides, while two others are classified as suspicious sudden deaths," spokeswoman Evita Caldwell

"We have nothing further to provide," she said in an email.

Here is what we know of each of the young victims:

Kayden Johnson, 2

Homicide still needs your help to solve the double homicide of a 2-year old & his 18-year old mother in the 5900 Block of Ferris on 4/30/19. Anyone with info can contact @STLRCS @ 866-371-TIPS(8477), Homicide directly @ 314-444-5371, or submit tips on the SLMPD Mobile app. pic.twitter.com/FeAXQXtdZP — St. Louis, MO Police (@SLMPD) May 7, 2019

The first victim, Kayden was also the youngest. The boy was killed April 30 along with his 18-year-old mother, Trina'ty Riley, police said.

Kayden and his mother were found dead in a home around midnight after police responded to a shooting call, according to a police report.

Kayden's father, Elijah Johnson, told CNN affiliate KMOV he was devastated. He received a call on his way to work telling him that his son and mother of his child were killed.

"Just a lot of pain, it was unbelievable. I could not believe it," Johnson told the station. "Mixed emotions, very heartbroken right now actually."

Johnson said his son was a happy child.

"He was uplifting, he was always smiling," he said.

Kristina Curry, 16

Kristina Curry, 16, was shot and killed in May.

Kristina was found dead near Roosevelt High School on May 23 after suffering apparent gunshot wounds.

The teen had been attending Roosevelt a month before her death but had recently dropped out of school, grandmother Antanina Valentine told KMOV.

Valentine couldn't comprehend her granddaughter's violent end, she said.

"I hurt because I can't understand why someone would hurt my granddaughter that way," Valentine told KMOV.

Jashon Johnson, 16

16-year-old Jashon Johnson was found dead of a gunshot wound near Fairground Park in June.

Another teen, Jashon was found near Fairground Park in the O'Fallon neighborhood on the night of June 8, after suffering multiple gunshot wounds.

When police arrived just after 10:30 p.m., he was not conscious or breathing and was taken to a hospital, where he was pronounced dead.

Kennedi Powell, 3

Fewer than 24 hours later, Kennedi was shot and killed 3 miles away from the spot where Jashon was found. At least one other child, a 6-year-old girl, was shot in the same incident, a police report said.

Kennedi had a big personality, her family said.

Kennedi Powell, 3, was shot and killed in June.

"She was beautiful young lady. She was the type of person who liked to play a lot, like to run off and pinch you," grandmother Tracy Waffard told CNN affiliate KMOV . "There's nothing that's going to bring her back. Every time I look out here on the ground, I see her, and it's hard -- real hard."

Tanisha Smith, the mother of the 6-year-old girl injured in the shooting, told CNN affiliate KTVI she feels the area is no longer safe for children.

"The streets are not safe no more, not even for your kids," Smith said. "This is a war zone now."

Charnija Keys, 11

Charnija is one of the cases being handled as a suspicious death, according to St. Louis police.

Officers responding to a shooting call found the girl just before midnight June 11 with an apparent gunshot wound to her head, police said. Paramedics took her to the hospital where she was pronounced dead.

A child abuse unit and homicide detectives are taking part in the probe, police said.

Myiesha Cannon, 16

Myiesha's is the other death authorities are classifying as suspicious.

The girlwas found with an apparent gunshot to the head just after midnight June 12, and she was transferred to the hospital where she was pronounced dead, according to police.

Derrel Williams, 15

Derrel Williams, 15, died at the hospital after suffering multiple gun shot wounds in June.

About two weeks later, officers responding to a shooting call found Derrel on the northside of the city June 25.

The teen was taken to the hospital in critical condition where he died after suffering multiple gunshot wounds, a police report said.

Eddie Hill IV, 10

Eddie Hill IV, 10, was shot and killed in July.

On July 19, Eddie was found dead by police responding to a drive-by shooting. The 10-year-old had been sitting outside with family on his porch when a dark blue SUV drove by and opened fire, KTVI reported

"It's really hard to deal with, especially someone young," Kaprice Hill, the boy's aunt, told KTVI.

Rachel Kemp, Eddie's mother, added, "It can cause so much pain and suffering to their family and it's unimaginable."

Xavier Usanga, 7

Xavier Usanga was shot and killed while playing with his sisters in his backyard.

Xavier was playing with his sisters in the backyard of their home in the Hyde Park neighborhood August 12 when he was killed, police said.

The boy was hit when two men exchanged gunfire in a nearby street. An 18-year-old black man was also shot but survived, police said. A gun was recovered at the scene.

"The bullet went through my son's throat and then grazed my daughter's elbow," Xavier's mother, Dawn Usanga, told KTVI.

Xavier was supposed to start second grade the day after he was fatally shot, his mother told the station.

A suspect in Xavier's death was later arrested, though police did not provide additional details to KTVI, citing an ongoing investigation.

The mother spoke directly to her son's killer, telling KTVI: "You killed my son and I know you see him playing and I hope his smile will burn in your brain forever and you know you killed my son."

Jason Eberhart, 16

Jason, 16, was shot multiple times in the Carr Square neighborhood August 18, police said. Another victim, an 18-year-old black man, was shot int he buttocks and survived, they said.

Charles Shelton, 49, one of Jason's cousins, told the St. Louis Post-Dispatch that the family was expecting big things from the teen.

"He had a lot of potential," Shelton told the paper. "We were looking for him to go somewhere. The plan was for him to follow his big brother in football."

Jason's brother plays for Ball State University, and his father is a former University of Illinois player who has coached in the St. Louis area, the Post-Dispatch reported.

Jurnee Thompson, 8

Jurnee Thompson was killed Friday outside a high school football game.

Jurnee Thompson was killed Friday night while at a football game with her family.

Two teenage boys and a woman were injured outside the preseason high school football game at Soldan High School.

Police officers were already in the area when the shooting happened and were clearing crowds after fights were reported, St. Louis Police Chief John Hayden said

"The little girl wasn't doing anything wrong," Hayden said. "She was with family when this occurred. Shots rang out. Not sure what particular fight that was going on when shots rang out."

Mayor Krewson asked during a Saturday news conference that anyone with information come forward because "conventional policing tactics are not enough."

Sentonio Cox, 15

Police responding to a missing person call arrived in the Carondelet neighborhood to find Sentonio dead from a gunshot wound early Sunday morning, authorities said.

A teenager who identified himself as a friend of the victim told the Post-Dispatch that Sentonio was headed home when he was shot. To get home, the teen often cut through an empty lot near the site of the shooting, the friend told the paper.