A Broome man who used cable ties to restrain very young Aboriginal children he believed were trespassing on his property was found guilty of assault on Friday in Broome Magistrates Court, but received only a fine and a spent conviction.

Matej Radelic, 46, used cable ties to restrain a six-year-old girl and two boys, aged seven and eight, at a home in Cable Beach in March. The children were found swimming in the pool in the front yard of the house.

The three young children were in tears, and video taken of them by passers by who urged Radelic to release them sparked an outcry when shared on social media.

During the trial the court heard police took 37 minutes to arrive at the home after being called by Radelic, despite the property being a five-minute drive from the station.

It also emerged that the 000 operator classified the call as priority three, which was a factor in the slow response.

When officers arrived at the home, they found two of the children still restrained. The third child had fled but was found shortly thereafter.

Radelic told media outside the court on Friday that he blamed the police. His lawyer had told the court he contacted 000 immediately after restraining the children and had told them the children's wrists were zip-tied, but he was not told to remove the restraints.

St John paramedics examined the children before they were reunited with family on the day of the incident.

Radelic's lawyer argued the use of the zip-ties was reasonable and necessary.

Police prosecutor Mícheál Gregg argued that while Radelic may have carried out a lawful citizen's arrest, it was unreasonable for him to have cable-tied the young children who had been compliant with his instructions.

Sergeant Gregg described Radelic's actions as having a "dehumanising effect" on the children and the use of the restraints were not the only option available to him at the time.

"(it) catapults it into the unreasonable," he said.

Both parties agreed that the young children had trespassed by swimming in the pool.

Radelic argued in court he was protecting his property, which had been broken into four times in two months leading up to the incident, with more than $10,000 of damage done on a previous occasion when pavers from the pool area were launched into windows.

The individuals who caused that damage were never identified, and there is nothing to suggest the young children who were restrained by Radelic were involved in the damage in any way.

Magistrate Deen Potter said the children's distress was clear.

He said the images circulating of the children bound together had been "seen in the historical context", which had a "destabilising effect in the community."

The ABC reports Magistrate Potter said the incident had "a marked impact" on the children and their family.

"While he was on the telephone he described the children as being scared and crying," he said.

"Their distress should have been an indication. Therefore at some point... (it must have) become blatantly clear that the continued application of force must have become unreasonable. There's an inescapable fact that the children were very and clearly distressed by their captivity."

Radelic was found guilty of two counts of aggravated common assault. Magistrate Potter found Radelic's use of force was unreasonable in relation to two of the children, while acquitting him of the third charge. He was fined $2000, with the fine suspended for 12 months, and given a spent conviction.