TWO children found dead in their rural home were allegedly drugged before being smothered, an autopsy has revealed.

Aussie brothers Max, 6, and Sam Johnson, 7, were found dead on May 5 – with their grandma arrested at the scene.

A post-mortem examination has found traces of prescription drugs in the boys’ systems, according to the Daily Telegraph.

Police allege their grandma, Kathleen Heggs, 66, gave her grandsons the medications before suffocating them with a pillow.

Heggs allegedly sent a text to authorities saying the two boys were dead and that she planned to take her own life.

When cops arrived at the scene, they found the boys dead in separate rooms and Heggs with self-inflicted injuries.

She was arrested and taken to the mental health unit at Orange Hospital before being transferred into custody.

On May 21, Heggs was charged with two counts of domestic violence murder.

The siblings were reportedly sleeping when the alleged murders occurred.

Heggs, the sole carer for the boys, moved with them over a year ago to a home on the outskirts of Coonabarabran in rural New South Wales.

According to The Sydney Morning Herald, the move was prompted after the woman “witnessed an incident involving her family too graphic to publish details of, and became known to police as a victim of crime”.

The boys’ dad told the Daily Telegraph that he and his partner had trusted Heggs to care for the children, as they were both struggling with mental health issues.

The couple had not seen the children for five years before their deaths.

“This is not how we were meant to get them back,” he said.

“We are completely broken… but those boys deserve a good send off, and that’s what we are going to give them.”

The boys will be buried wearing their karate uniforms, each with a yellow belt they were due to earn the same week their lives were tragically cut short.

A family friend, who has a son the same age as the boys, said he would see them at karate lessons, football matches and school.

He said there were no clear signs the family was struggling, describing Heggs as a “beautiful lady” and the boys as “cute little kids, full of energy”.

He said locals have been really hard-hit by the news.

“This is a tragedy, and it’s affecting so many. Petty crime happens and that, but it’s a very safe community, we don’t have problems like the cities.”

It comes as investigators found human remains on Friday in the search for Aussie teen Pheobe Bishop, who vanished three weeks ago.

Pheobe’s two housemates James Wood and Tanika Bromley were charged with murder on Thursday, along with two counts of interfering with a corpse.