A teacher performing a routine check of students' backpacks at Oak Park Elementary on Tuesday morning found a loaded 9mm handgun in one student's bag, officials said.
The gun was taken, and officials notified the 5-year-old child's parents after the discovery at about 10 a.m.
An investigation shows the child's parents put the gun in the backpack while running errands over the weekend and forgot to take it out, Police Capt. William Jackson said.
Jackson said police have possession of the gun.
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Prosecutors will present the case to a grand jury as a matter of concern, he said. A possible criminal charge is possession of a firearm on school property, he said.
Because of the "extraordinary circumstances" in the case, Jackson said, all police reports will be turned over to Child Protective Services and Jackson County Youth Court.
Ocean Springs police were on the scene within five minutes, Schools Superintendent Bonita Coleman said. She declined to discuss what action was taken, citing privacy reasons.
"First and foremost, the lesson here is that being a responsible gun owner means securing your weapons," Coleman said. "That is the lesson here. Gun owners should secure their weapons, and they should not be available for little children. Period."
Some parents and others turned to Facebook to say they were going to check on their children. Others made posts saying backpacks should no longer be allowed at school.
"That's not the answer," Coleman said. "The answer is securing weapons."
Coleman said teachers of young students routinely pull lunches and juice boxes out of their backpacks.
"The teacher who found it immediately notified her principal, who immediately notified our school district police officer," she said. "The gun was secured quickly."
The school district activated an automated telephone message to advise parents of the situation, Coleman said.
It's at least the second time a gun has been found on a Mississippi Coast school campus since March 9. That's when an eighth-grade student took an "airsoft" gun to a Biloxi school and showed it to another student.
At least 15 schools across South Mississippi have confirmed reports of threats and alleged plans for a school shooting since the deadly Valentine's Day shooting at a school in Parkland, Fla. Broward County sheriff's officials say Nikolas Cruz, 19, slaughtered 17 teens and adults with an AR-15 semi-automatic rifle at Marjory Stoneman Douglas High School.
South Mississippi schools have gone on lockdown, with heavy police presence, during perceived threats reported since the Florida massacre. One superintendent has blamed the scares on social media.
Just a week after the Parkland shootings, a fifth-grade student at Bayou View Elementary was removed from campus after making a threatening comment.
The Oak Park incident marks the second time in three months that a Mississippi Coast child has brought a gun to school. In December, a student at Pass Christian Elementary was found at school with a gun.