Children who opt out are sent to other classrooms to work.
Mr Warren and Ms Muirhead have both kept their children in the classes because they did not want them to feel isolated from their classmates.
Mr Mudannayake, a Buddhist, said he wanted all religions to be taught, the classes to be held out of school time, or the lessons to be stopped.
If the school did not adjust the policy, Mr Mudannayake said he too would make a complaint to the Human Rights Commission.
Mr McCarthny would not confirm whether the school was considering changing its stance on the classes.
"All mediation is confidential until a decision is made," he said.
But a statement from the school late today afternoon said all options were being considered.
"The school principal, Craig McCarthny, confirmed that he had a productive meeting with the parents and listened to and discussed their points raised about the programme.
"He told the parents that because the issue is still under mediation before the Human Rights Commission between the board and a school parent, the board is subject to confidentiality and therefore he could not discuss board deliberations, other than to say the Board was looking at all options."
Mr Warren's complaint has gone to mediation with the commission.
He said today he did not understand why the school needed so much time to make a decision.
Ms Muirhead said she hoped Mr McCarthny was taking the parents' concerns seriously.
"There is a growing group - almost every day I get contacted by other people sharing their support or sharing their own experiences, both at St Heliers School and at other schools around the country as well."
The complaints to the Human Rights Commission claimed the classes were discriminatory by excluding children from their friends on the basis of religious belief for the period of the class, making the children feel ostracised and different.
The Secular Education Network, which is supporting the parents, said the Churches Education Commission was believed to provide voluntary teachers for about 700 of the country's 1800 state primary schools.
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Religious instruction in state schools
* Teaching must be secular during the hours a school is open for instruction
* Schools can close for up to an hour a week to a maximum of 20 hours a year for religious instruction or observance
* Children can opt out of classes if parents don't want them to take part
(Source: Human Rights Commission)