"We have a wide range of ages and abilities. We don't worry too much about that."
The children spent the first part of the day indoors, playing games that teach skills like dribbling or passing.
For the last hour they had a mini tournament, in teams of four to five, outdoors.
Calvert co-ordinates the programme, advertises it, gets equipment and takes registrations.
His young helpers, Amy Haughian, Kate McPherson and Oliver Hutchins, are "very relatable" to the children and they run and lead the activities.
Rutherford Junior High School has indoor and outdoor turfs the programme uses.
After the holiday programme comes a one-day Football Festival on October 11. It will be a whole-day tournament, 9am to 3pm.
Calvert arrived in New Zealand in 2016, and is the goalkeeper for Whanganui Athletic.
Football isn't as big here as it is in England, where he comes from.
"Kiwis just don't get the professional side somehow."
An increasing number of people here are playing the game, but for 80 per cent it's purely social, he said.
The volunteers are many and brilliant, but lack the resources or ability to get it to the next stage.
In the past five years, the number of children playing the sport has gone up "massively".
"The biggest part that has grown has been the girls-only pathway within the sport. Numbers of girls have gone up 50 per cent."