The company was "pretty concerned" when the matter was first brought to its attention, she said. An investigation process was launched and the parents notified.
Following that investigation and subsequent disciplinary process, Mrs Roy no longer worked at the centre, Ms Hughes said.
"She both breached the early childhood regulations and our behaviour management policy and practice."
The child had returned to the centre following the incident, she said.
"We restored the family's confidence when we explained the process and our findings, so they returned the child to the centre, and we also offered some professional support, which they didn't take up but it was offered."
All the other teachers in the room denied following Mrs Roy's example, Ms Hughes said. However, the Teachers' Council was told other teachers in the centre had picked up the threat and used it to scare the boy from putting things in his mouth.
"The use of Sellotape was adopted as a practice for dealing with this behaviour by other staff, who said things to X such as that they would stick his mouth together with Sellotape or use the Sellotape if he put toys into his mouth," the council heard.
Ms Hughes said all teachers at the centre had been given refresher training on how to deal with difficult behaviour.
"We felt that because she was leading that room, that obviously she had an influence on what teachers understood to be right and appropriate," she said.
"So we went about making sure they understood our behaviour management policy, explained our expectations, told them what wasn't ok, and made sure they fully understood what we expected going forward."
Ms Hughes said she was "absolutely confident" a similar incident would not happen again in a Best Start centre, and that parents should feel safe leaving their children at a Best Start facility, and in particular Top Kids New Lynn.
"I believe so," she said.
"The centre has a good reputation in the community and it's well occupied. I'm very confident that it is a good operation."
Peter Reynolds, chief executive of the Early Childhood Council, said taping a child's mouth was "totally unacceptable, no matter what the circumstances".
"In our view this teacher is extremely lucky to still be registered, but we are not unhappy with the result as it stands," he said.
Childcare teachers often dealt with children with challenging behaviour, he said, and most 4-year-olds would be able to rationalise and understand good behaviour from bad.
"If this child is acting out, then ensuring clear expectations, a good working relationship with the child and working with parents is most appropriate.
"If this child has more significant underlying issues, then the input of another professional would seem appropriate."
However, Mr Reynolds stressed "teachers are human too".
"Everyone has a stress point. It is advisable when a teacher hits the wall that they distance themselves from the problem and consult a colleague or their manager for help. In no way should they take physical action such as this on a child."
The child, known as X in the tribunal's decision, had been attending the centre for two years, and had a history of putting things in his mouth, which posed a safety hazard particularly for choking, the council heard.
When he was 3, he swallowed paint used in art work, and in another incident he told staff he had swallowed a pin. An x-ray revealed he had swallowed a plastic peg.
In February 2014, the boy was sitting at a table playing when a staff member realised he had put a toy in his mouth. He ignored instructions to take it out, so the teacher went to Mrs Roy.
She "quickly went to take tape from the drawer and put a length of tape over X's mouth while the toy was still in X's mouth", the council heard.
"Because of the narrowness of the tape, X could still open his mouth so [Mrs Roy] put another bit on his lip. She told X that if he put toys in his mouth again she would use a bigger piece of cellotape next time."
She then told him putting toys in his mouth would give him a sore stomach.
All of this was done in front of staff and other children.
Mrs Roy, who had 14 years experience as a teacher at the time, said she had done it so the boy and other children would learn.
Before the incident, she had threatened to stick tape over his mouth three or four times, the council heard, and the practice went on for around two to three weeks.
"The use of cellotape was adopted as a practice for dealing with this behaviour by other staff, who said things to X such as that they would stick his mouth together with cellotape or use the cellotape if he put toys into his mouth," the council heard.
When she was initially confronted, Mrs Roy said she was "guilt-free" and had taken steps to save the child from swallowing a toy.
However, by the time her case came before the tribunal, Mrs Roy said she accepted her actions constituted serious misconduct for being physically abusive and bringing discredit to the teaching profession.
She had completed more than one educational training programme related to the appropriate disciplinary procedures for teachers since the incident, she told the tribunal.
The Teachers' Council ruled her actions were "entirely inappropriate and amounted to serious misconduct", but put it at the lower end of the scale.
Mrs Roy was censured and ordered to pay costs of $1154.
