Announcing the charges on Thursday, Australian police said they were becoming increasingly concerned about the growing number of teenagers becoming radicalized in the country.
"It's disturbing that we are continuing to see teenage children in this environment," said Catherine Burn, NSW Police deputy commissioner for special operations.
"We are charging a 15 year old with a very, very serious offense. This is an offense that has a maximum of life imprisonment. This is concerning not only to us, in law enforcement, this should be concerning to everybody," she added.
The Australian Federal Police's (AFP) deputy commissioner for national security, Michael Phelan, said two of the suspects -- a 20-year-old man and the teenage boy -- had been arrested during Thursday's raids and later charged with one count each of conspiracy to conduct an act in preparation for a terrorist act. The AFP said that three other men, one aged 21 and two aged 22, were already in custody and faced the same conspiracy charge.
One of the 22-year old men was scheduled to appear before a Sydney local court on Thursday afternoon. The other two men had been refused police bail and are scheduled to appear in court to face the charges on Wednesday, 16 December, according to an AFP statement.
Phelan said the five men were part of a "radicalized" group that were allegedly planning attacks on specific government buildings in Australia, including the AFP headquarters in Sydney.
The charges stem from a broader investigation, called Operation Appleby, and relate to documents seized in raids conducted across western Sydney in September and December 2014, as well as physical and electronic surveillance.
The alleged plan to target government buildings was the second specific plot identified in these raids. Charges have already been laid against the organizers of the the first plot, which police said involved plans to target a random member of the public.
"It started last year with an alleged terror plot to conduct an attack in Sydney, and with the additional charges today we are saying that there was a further alleged plot that was going to be undertaken In Sydney," said Phelan.
Disturbing to deal with teenage children
Police said the teenager arrested on Thursday had been 14 at the time the alleged terror plot was planned, and although they didn't know the exact details of any role he would have played in implementing the plan, they said it was "concerning to everybody" that a child this young was involved.
When asked about the parent's reaction upon the boys arrest, Phelan said he understood that the parents were "very cooperative."
Burn said the boy had been known to police since the 2014 raids and that they had been working with him and his school prior to his arrest, but they did not know how he had become radicalized.
"A lot of the people that we are dealing with, and emphasizing that it's a only a small group of people, are clearly radicalized," she said. "They are clearly radicalized to the point of talking about and acting out with violence. How they have become radicalized we don't actually know, we don't know how the 15-year old has got to the point where we will allege he got to."
Burn later confirmed that the group of five who have been charged were "associates" of a separate 15-year-old boy who shot dead an AFP accountant outside police headquarters
in Sydney in October 2015.
Phelan said that the "whole Appleby crew" had been influenced by people overseas, and that those people had come in and out of Australia. He said they had "the capability and the intent to carry out an attack, here in Australia" but that there was also enough intent domestically to execute the plot without their involvement.
He emphasized that police did not believe that the alleged plot was in any way organized by ISIS, but said the police were working to try and stop the radicalization of youth at its source.
"Paths to radicalization are different," he added. "People are inspired by things that occur offshore, either directly or indirectly, and also inspired by people here domestically."
"The key partner in all of that to identifying radicalization, and to help us and indeed the community in this process, is people like the parents and teachers and those that have day to day interaction with the young people. It's important that if people identify things that are different, things that are outside the norm to try and intervene as early as we can."