The mother of one of the boys said her four-year-old son was left traumatised and covered in his own sweat and urine after he became trapped on the bus in Mudgee for the entire school day. 

The driver, Grayson Gene Tuck-Lee, pleaded guilty to leaving a child in a motor vehicle causing emotional distress before Magistrate Terry Lucas on December 7. He has lodged an appeal against the severity of his sentence, which includes a $1000 fine, and is set to appear in Dubbo District Court on February 16. 

The mother, who cannot be named for legal reasons, said the experience has left her son with a fear of buses that requires counselling.

"Finding out that he is appealing the $1000 fine is a total slap in the face," she said. 

Mr Tuck-Lee said he was still considering whether to proceed with the appeal. He said he did not lodge it to escape the fine, but to seek a downgrade a criminal conviction which would impact on his other business as a contract mechanic. 

He said the two boys were not seated in the pre-school area in the front of the bus when he parked in a busy bus depot, and had hidden down the back of the vehicle.

"My mistake was not checking the bus when I parked," he said. "The doors were not locked, all they had to do was press a button."

He claimed he had since been harassed by the mother over the incident, while the other family involved had not expressed concerns over how it was handled.

"The had a full on f----n' fun day in the bus, sitting in the drivers chair and playing with the panel, and I'm copping it for it," he said. 

A company spokeswoman said the the incident was an error by a fill-in driver. 

"He is no longer driving, procedures are now in place so that it cannot happen again," she said.

"Assistance has been offered to the families involved and the matter has been dealt with by the proper authorities." 

The mother, who lives seven kilometres from Mudgee, said her son caught the bus as normal with his two siblings at around 8.30am on October 24.

She said all of them were travelling to their schools at Mudgee, where the 49-year-old driver dropped off most of the students, except for the two pre-schoolers who were due to attend Mudgee pre-school, 500 metres down the road from the local public school. 

Instead, the mother said Mr Tuck-Lee drove 2.7 kilometres to the bus depot where he parked the bus, leaving the two pre-schoolers inside. 

The mother told Fairfax Media the boys were too scared to shout out for help or eat their packed lunches, because they are not allowed to shout or eat on the bus and thought they would get in trouble. 

The pair sat themselves in the "naughty chair" and drank water before another driver found them "distressed" six hours later at 2.30pm. 

The mother said instead of calling an ambulance, the bus was driven back to Mudgee Public School by another driver where she found her son covered in sweat, smelling of urine and "pale and splotchy from crying".

"I had to throw his clothes out, and to have multiple showers to get the scent of urine off of him," she said. "He's just terrorised from it." 

The mother said the pre-school had failed to notify her that her son had not shown up to class. It has since changed its policy. 

"He started kindergarten on Thursday and leading up to this week the nightmares are getting worse," she said. "It's just horrific." 

The mother said Mr Tuck-Lee had called her to apologise, but "sorry really doesn't cut it".

"Thankfully it was only 24 degrees," she said. "He could have been ringing me to tell me that my son was dead." 

Mr Tuck Lee said the mother had hung up on him when he called to discuss the incident. 

with Georgina Mitchell