The four children found dead alongside their mother and grandmother in an upstate New York home appeared “happy” during their final conversation with their heartbroken father, he revealed Friday. 

Brady Harmon recalled the last time he spoke with his kids during a roughly 15-minute Facetime call on June 7.

“They seemed like happy little kids,” he told The Post. 

Mechanicville police discovered the corpses of Harper Harmon, 13, Hudson Harmon, 11, and twins Gavin and Gracelynn Harmon, both 10, inside an apartment Tuesday, where investigators believe their grandmother fatally poisoned them and their mother, Sarah Myers, 44.  

“Harper and Grace would show me their drawings, Hudson would show me their cat and Gavin would show me something he built,” the grieving dad said.

Harmon, 46, hadn’t seen his kids since 2019, but had recently been granted two months of custody – which was set to begin July 1. 

“I was supposed to be flying out on the 30th, gathering my kids and flying them home, then having them there for 60 days,” explained Harmon, who lives in Salt Lake City, Utah.

As he was preparing for their arrival, local cops knocked on his door late Tuesday to break the unthinkable news.

“They say time heals all wounds, but this is a gaping hole that will never heal … it will never go away,” he mumbled, his voice cracking. 

The plan is to bury his children in Utah – far away from their mother, Harmon told The Post. 

“I don’t believe anyone who can’t protect them should be anywhere close to them. If she had anything to do with it, that’s just another reason why,” he said of his ex-wife – adding that the arrangements are part of his “responsibility and duty as a parent.”

Old heart-wrenching photos shared by Harmon on Facebook show the smiling children clad in butterfly and dinosaur costumes for Halloween, playing on a swing-set and cuddling with their father during a nap on the couch. 

The children’s maternal grandmother, Amy Steadman – whom police believe may have carried out the suspected mass poisoning – had lived with the family at one point during Harmon and Myers’ decade-long relationship, he said.  

“She was never really a cordial, warm person to be around … it was very arm’s distance, I guess,” Harmon said of his former mother-in-law. 

Still, she appeared to have a close bond with the children. 

“She was just a doting grandma, you know, she’d spoil the kids – the grandkids,” he added. 

A hand-written note discovered inside Steadman’s Harris Avenue home – where responding officers couldn’t identify the bodies because they were so badly decomposed – “strongly suggests” that the grandmother was “involved” in the deaths, Mechanicville Police Chief Bill Rabbitt revealed during a press conference Thursday. 

One of the children was stabbed, while the rest appear to have been poisoned – possibly in a fit of rage after Steadman allegedly became resentful over Harmon’s recent custody win, sources told Channel 13.

“There is recovered evidence from inside the apartment indicating intentional poisoning — to include numerous prescriptions and over-the-counter medications,” Rabbit said.

“Evidence recovered during the investigation, including a handwritten note, and other circumstantial evidence, strongly suggests that Amy Steadman was involved in the deaths.”

Syringes were found inside the home and investigators believe the children may have been injected with drugs, sources also told the outlet. 

Investigators were “awaiting results from the crime lab and other investigative findings before releasing more details” Friday, Rabbitt told The Post, as the probe continues.