"They just love it," she told the Rotorua Daily Post.
Mrs Mills' daughters Waiora, 10, and Atawhai, 8, both played tennis through the programme and her elder daughter Tepora was a Hot Shots assistant.
"She's been helping out since she was 11 or 12," Mrs Mills said.
Another daughter, 6-year-old Maia, would play tennis this summer with her sisters. She already swam and took ballet classes.
Younger children used a larger ball, smaller racquet and played on a smaller court.
Mrs Mills said although the children kept fit and met new friends through the sport, the most important benefit was their enjoyment.
Tennis New Zealand participation programmes manager Jenny Fitzmaurice said it was particularly important to make the programme fun.
"Fun is key to children's sport, particularly in these early years.
"That's why both of these programmes are about kids having fun while they learn the basic skills and get used to being in a tennis environment."
The Hot Shots programme is run by 200 tennis clubs around the country and is designed for children up to 12.
As children improved, the courts and racquets get bigger and the balls bouncier.
Children play on a full size court from the age of 9.
Rotorua Tennis Club recently acquired a new coach, Justin Megraw, who has played professionally and has 20 years of coaching experience.
"He's an absolutely amazing coach with the kids," Ms Dowland said.
The club is holding an open day for new families on Sunday, October 15 from 1pm-3pm.
Over the spring and summer, coaching sessions will be held on Wednesday afternoons and games on Fridays.
