A 4-year-old Harris County boy died after shooting himself in the head Tuesday, adding to a toll that's become the second leading cause of accidental death for children in Harris County.

Only motor vehicles account for a larger percentage of accidental deaths, according to Harris County Institute of Forensic Science statistics. Of the 1,074 minors who died in Harris County from 2011 to 2014, about 1 in 8 was killed by a gun, according to the data.

That's an average of 27 child fatalities by guns a year for that span.

Two minors have already died from accidental gunshots in 2016 - Bryson Hernandez, who shot himself in the head at his grandparents' Cypress-area home early Tuesday, and a 15-year-old who was shot by his older brother on Jan. 16 in southwest Houston.

In addition, a 2-year-old in Montgomery County shot himself in the hand after his father left a handgun he'd been cleaning out unattended on Jan. 3.

Everytown for Gun Safety, a gun control coalition funded by former New York City Mayor Michael Bloomberg as part of a crusade against firearm violence and to politically challenge the National Rifle Association, tracks media reports about accidental shootings by children. Recently released data compiled by the organization shows that at least 265 minors unintentionally shot themselves or someone else in 2015, and 17 of those incidents were in Texas.

The group found that improper gun storage led to most of the unintended deaths. Two-thirds happened in a home or vehicle belonging to the victim's family and most often with legally owned guns that were not secured.

Child Protective Services officials are looking into how Bryson gained access to the firearm. Bryson's grandparents are cooperating with investigators fully, according to the Harris County Sheriff's Office. The findings will be forwarded to a Harris County grand jury.

Adults can be prosecuted for making a firearm accessible to a child, a misdemeanor charge.

In a statement released through Children's Memorial Hermann Hospital, relatives said they hoped Bryson's death would spur gun owners to take more precautions.

"Always check to make sure you know where your guns are and that they are safely out of reach of children, not loaded and locked away," the statement said.

Bryson, who was enthralled with the fearless and beneficent superhero Iron Man, will save the lives of other children as an organ donor. He will be laid to rest in his Iron Man costume.

Houston-area CPS spokeswoman Tiffani Butler said children should be taught not to touch guns. If minors encounter a weapon, they should know to leave the area and alert an adult.

She also provided these tips from the agency's Office of Child Safety as ways to prevent children from accessing a loaded gun:

Keep guns unloaded when not in use.

Don't store bullets and guns in the same place.

Use cable locks or trigger locks.

Use gun locks with combination, magnetic or electronic security, but not keys.

Store guns in a lock box, vault or safe.

Bryson's autopsy was scheduled to be performed on Friday.