"Obviously the grandparents are looking after them on the parents' behalf."
Students get about 12 weeks' holiday each year, whereas most workers are entitled to four weeks' annual leave.
During school holidays, many parents must decide whether to take days from their leave allowance to look after children.
Business NZ says the best way to manage leave is to file requests as early as possible.
"School holidays are set out at the beginning of the year," chief executive Phil O'Reilly said.
"So, getting in early is key."
Employees had to communicate with each other and their managers about leave.
"Obviously, there's always a lot of people who want time off around school holidays," Mr O'Reilly said.
"For example, if you've got a group of employees, and three of them have kids, one might say, 'I want to take the May school holidays away' and the other one might say, 'Okay, I'll take the August ones'."
The Engineering, Printing and Manufacturing Union, which represents more than 4000 New Zealand workers, recommends a ballot system be used if too many leave requests are put in at the same time.
"If a number of people are seeking it [leave], then you go into a ballot," spokesman Mark James said. "So you are balloted for that time off."
He stressed the importance of planning ahead, as most issues could usually be worked out if enough notice was given.
About one month ago, a member's case was referred to the union after the man's Christmas leave request was denied, Mr James said.
"The boss said he couldn't allow him that time off because he'd be the only suitable person on site to operate the forklift.
"We said, 'This far out. Why aren't you training someone else ... so then this worker can have the time off'."
After negotiations, the employer agreed to grant leave and train someone else for the role, Mr James said.APNZ