Dr Bates urged parents to have their children immunised against chickenpox.
"There is a cost for this vaccination that I know some families will find hard to meet, but for those who can afford to pay the fee charged by GPs, I would urge them to do so. The chickenpox vaccination is available to children from the age of nine months."
Dr Bates said hospital staff "weren't surprised" that two children needed intravenous antibiotics.
"It's widely known that one in 20 New Zealand children will develop a bacterial skin infection as a result of their having chickenpox, and that one in 10 children hospitalised with chickenpox will be admitted to Starship Hospital's intensive care unit.
"Chickenpox is a serious disease that spreads easily through contact with family and friends. It can cause inflammation of the brain, permanent scarring and, at its worst, death."
Mrs Mahony said she and her husband would have vaccinated Isaac if they had known they could.
"If we'd been made aware that a vaccination against chickenpox was available at the time of his other standard immunisations from Plunket, we would not have hesitated in having it done," she said.
"You wouldn't wish this illness on any child."