Grubbs -- a former Language Arts teacher at Bradley Middle School -- is accused of molesting one of his students. School officials said Grubbs resigned his position in May.
Police said it happened while inside the school, during school hours and afterward.
Parents are appalled.
"That's scary. You don't think that something like that would happen from a teacher," said parent Wendy Caracciolo.
Huntersville police are trying to figure out just how many students were sexually assaulted inside the walls of the school.
"There are allegations from three to five children that we need to look into," said Lt. Ken Richardson.
Richardson said the 12-year-old told police he was also molested on a trip to Myrtle Beach.
Grubbs took other children there as well and officers are now investigating those claims with Myrtle Beach authorities, said Richardson.
"You hope you never have to work a case like this," he said.
Grubbs' neighbors said he seemed friendly and they wouldn't expect this.
"My little girl has been over there planting tulips. She was never out of sight, thank goodness, but just to think that she was that close to someone doing this to children," said parent Aprilia Lane.
Grubbs paid a $150,000 bond and is out of jail Wednesday night.
As Huntersville police interview more of Grubbs' students, they said they expect more charges will come out of their investigation.
Officials said Grubbs does not have a criminal record.
Huntersville police said Grubbs is the founder of a non-profit group called "Swinging With Kids," which raises money for children's sports.
Investigators said they're trying to learn more about that group.
It is alleged they found enough explosive material to blow up five suburban blocks.
Amundsen has been remanded in custody and will appear in court tomorrow over the new charges.
Detective Police Superintendent Paul Wilson says it is the first time anyone in Queensland has been charged with terrorism offences.
"These charges emanate from the Commonwealth Criminal Code, and the charges are an act done in preparation for terrorist acts; using a carriage service to make a threat; using a carriage service to make a bomb threat - that is a telecommunications device," he said.
"Further charges of fraud and charges under the explosives regulation will be also preferred in relation to this 40-year-old."
Amundsen faced the Brisbane Magistrates Court earlier this afternoon charged with fraudulently obtaining the explosives.
His lawyer Andrew Boe says his client is not a terrorist.
"I think the public should and the media should just drop the ante a little bit about being too preoccupied that this has got anything to do with terrorism. It hasn't," he said.
"He's not associated with any terrorist organisations, there is a completely plausible and non-nefarious explanation for the circumstances in which he finds himself."
Queensland Police Minister Judy Spence has told Parliament a large police task force has been formed to look into the incident.
"The task force comprising 40 detectives, including federal police, will continue to investigate the matter," she said.
"The ideal situation in any terrorist act is prevention. All
agencies involved should be congratulated for the good work."
Apparently he had the explosives for a "special effects" thing for a "movie".