The 13 siblings found starving and shackled inside their California house of horrors also had to march around for hours in the middle of the night, former neighbors told The Post on Tuesday.

“I thought they were like a cult,” said a man named Mike, who lived across the road from the allegedly abusive Turpin family in the town of Murrieta for several years before they moved in 2014.

“They would march back and forth on the second story at night. The light would be on the whole the time, and they would be marching the kids back and forth,” said Mike, who wouldn’t give his last name.

Mike works in a hospital and says he’d often see the Turpin siblings being marched through the upstairs rooms between midnight and 3 a.m.

Parents Louise and David were arrested in the nearby town of Perris after police Sunday found their offspring — ages 2 to 29 — malnourished and living in squalid conditions, with several shackled to furniture.

But Mike says he and his wife, Myrna, never saw anything that prompted them to call the authorities — even if the huge brood across the street seemed a bit weird.

“My wife called them clones. They spoke robotically, in a monotone and at the same time,” he said of his spouse’s few interactions with the family at the local grocery store.

When the family moved out, he couldn’t believe how much trash they hauled out of the home.

“There were lots of black garbage bags,” Mike said. “I never saw any toys or bicycles.”

The family first moved into the Murrieta home in 2010, their former landlord Eric Aguirre told The Post. Before that, they owned a farm in Texas but fled when that was foreclosed on, court records show.

The trailer where they lived on that property, too, was filled with junk, neighbors said.

“I ended up calling the police because of the trash and everything that was left there,” said Randy McClain, who moved in across the road from their Rio Vista farm around 2005 and came by to see what was up after hearing dogs barking on the abandoned property.

“There was a brand new pickup truck covered in [trash] — a whole truck bed full and overflowing to the ground with trash: diapers, Spam cans, potted meat cans, just overflowing.”