Four children have been placed in state care and three adults have been charged as police continue to investigate the discovery of an eight-year-old boy allegedly imprisoned in a shed at a rural NSW drug house.

The boy's 26-year-old mother and two men, Bowdie Kliemann and Jacob Potter, have been charged and refused bail, after police found the boy in a raid on the remote Elands property, northwest of Taree, last Friday.

As well as finding the boy in two-metre-square room at the back of a detached shed that had no insulation and only contained a mattress and a bucket, police also discovered an elaborate hydro set-up containing 225 marijuana plants.

Two men have been charged. (9NEWS)

The boy reportedly told police that he had been locked in the shed for more than three weeks and suffered through storms and extremely high temperatures, and was only let out to do chores, the Sydney Morning Herald reports.

Three other children were found at the property, aged between 12 months and nine years old.

Neighbours told the Herald they never noticed anything was amiss, despite seeing the boy's siblings go to and from school.

"But not the boy, we hardly ever saw him," one neighbour told the Herald .

"There was definitely the other kids, and I'm not saying I never saw him, but it was rare and it was never close by."

Police said they found the boy on this NSW property. (NSW Police)

"We are totally shocked about all of this...We never put two and two together about the boy.

"I actually had trouble believing it until I read it online this morning, that opened my eyes up."

The NSW Police Child Abuse Squad is investigating the situation surrounding the children, Manning-Great Lakes Detective Chief Inspector Peter McKenna said.

“You don’t prepare yourself to come across these types of things, especially anytime you see a child put in danger like that, that is something that really hits home,” he said.

“We’re just very happy to get the ending that we did and the child is now in the care of the right people.”

A hydroponic set-up was also allegedly found on the property.

Inspector McKenna said the hydroponic set-up was one of the more sophisticated operations police had come across.

“During the search we found what I can only describe as a very elaborate and sophisticated hydroponic cultivation setup,” Detective Inspector McKenna said.

Police discovered a remote control switch which slid back the deck at the rear of the house to reveal two large trap doors.

“When we opened those trap doors there were ladders that went down to an underground cave, the cave was made out of three shipping containers that had been sunken into the ground and welded together, inside that setup we found 225 cannabis plants,” Inspector McKenna said.

“It is definitely one of the more sophisticated setups that we’ve ever come across and we were very surprised at the elaborate nature of it.”

All of the children have been placed in the care of the Department of Family and Community Services.