Three young children have been shot accidentally in the Houston area in the past four days, two fatally from self-inflicted gunshots.

In the latest incident, a six-year-old boy was taken to hospital in critical condition after being shot by his five-year-old brother on Monday morning in north-east Harris County, police told reporters.

On Sunday, Codrick Beal, four, shot himself with a gun he found while staying with a family friend at a house in a northern suburb, while his mother celebrated her birthday.

Beal’s death followed that of an unnamed three-year-old boy, who died after shooting himself in the head at home in north-western Harris County on Friday afternoon.

“It’s just a terrible accident,” Leticia Beal, a cousin of Codrick’s mother, Ashley Beal, told the Houston Chronicle. “We see it all the time on the news but you never think it’ll hit home. It’s the most horrible thing.”

Another four-year-old boy died in a shooting incident in the west Houston suburb of Katy last November. Ryan Welch was shot in the face by a .40-calibre Smith & Wesson pistol found in a closet in the master bathroom of his home next to a BB gun and a machete, the Chronicle reported. It was not clear whether the boy or his six-year-old brother pulled the trigger.

On Monday, the Harris County sheriff’s office said investigations into the two fatal shootings last weekend were ongoing.

“If you are going to keep a firearm in your home it should ALWAYS be stored in a locked safe, gun vault, or storage case AND out of the reach of children,” the office said in a statement.

“In addition to storing your firearm in a locked location, use gun locks for added safety. Ammunition should also be stored in a locked location separate from the firearm.”

Two years ago, the father of a four-year-old was arrested after the boy found a gun and fatally shot himself in the stomach in a north Houston apartment.

Police could pursue charges in the most recent shootings. Under Texas law, an offence is committed if “a child gains access to a readily dischargeable firearm and the person with criminal negligence: (1) failed to secure the firearm; or (2) left the firearm in a place to which the person knew or should have known the child would gain access”.

According to a report last June from the anti-gun violence group Everytown for Gun Safety, on average almost two children a week were accidentally shot and killed in the US between December 2012 and December 2013. The report found that 65% of those deaths took place in a home or vehicle belonging to the victim’s family and usually involved guns that were legally owned but not properly secured. Another 19% happened in the home of a relative or friend.

In Louisiana last month a three-year-old girl, Alexis Mercer, died after shooting herself in her family’s living room with a handgun her father had failed to put away after cleaning it.

In January a two-year-old in Florida died after climbing into the front seat of his family’s car, finding a gun in the glove compartment and shooting himself in the chest.

“Unintentional child gun deaths can be prevented: if fewer gun owners left their guns loaded and unlocked, fewer children would lose their lives,” the Everytown report said.