But despite his telephone pleas to Air New Zealand call centre staff and a manager, Mr van Gelder was quoted a price of more than $500 to have his family's old tickets exchanged for new ones.
"The whole way through, Air New Zealand was not helpful," he said.
Mr van Gelder said his wife, Imelda, flew home on her old ticket to save money, and the family are now apart during their holiday.
He said the airline waived $50 in booking fees but charged him $300 for new tickets for him and Jayden.
Mr van Gelder said his son appeared healthy, did not have a fever and would have been "hunky-dory" on the flight back to Christchurch.
He could have kept quiet and put his son on the plane without anyone realising he was ill, but instead tried to do "the right thing".
He had hoped the airline could have responded with a bit of compassion.
"I understand the conditions but why punish us with the extra costs?"
He said he would think twice about telling the airline the truth if the same thing happened again.
Air New Zealand spokeswoman Marie Hosking said Mr van Gelder and his family would have been irresponsible to have travelled knowing that their son had chicken pox.
She said the airline followed health recommendations.
"Chicken pox is highly infectious and standard advice internationally is that the ill person should be prevented from having contact with the general public. Travelling on any form of public transport would put other passengers at risk, particularly pregnant women," Ms Hosking said.
She said the airline recommended passengers take travel insurance to cover unexpected situations and that the family had opted out of doing so when they booked their tickets.
Mr van Gelder said taking travel insurance would have cost his family $20 a ticket and a total of $160. Air New Zealand said the total cost of insurance would have been $40 as they would only have had to pay $20 for each adult for the round trip and insurance for children accompanied by an adult is free.
Air New Zealand's main domestic competitor Jetstar would have done much the same thing.
Jetstar spokeswoman Andrea Wait said Mr van Gelder would have had the "change fee" waived but would have been charged the difference in the two sets of fares.
Have your say
What do you think? Should Air NZ have shown some compassion? Contact newsdesk@nzherald.co.nz