"Children are our biggest asset," said Mrs Rangi, who has three foster children under five.
"As parents, our kids' safety is paramount for us. That extends to all the children who ride with us. When they're in our cars, they become our babies. They're precious to their parents, and they're precious to us."
The Rangis say child restraints are particularly crucial, as Masterton Shuttles now does the school runs for Te Kura Kaupapa Maori o Wairarapa - ferrying 17 primary-age children to and from school.
"In those hours before and after school, those kids are our responsibility," she said.
"At those times, we're an extension of their family. If their parents are teaching them to wear seatbelts and to sit in their booster seat, then we're modelling the same thing for them.
"I would hate to think of anything happening to those children in our care. If we can eliminate the risks, we will."
At present, New Zealand law provides children be seated in an appropriate child restraint until their fifth birthday - however, from November 1, children will be required to use a booster seat until they are 7 years old.
The couple are currently seating older kids in booster seats, as guidelines from injury prevention group Safekids state that children are unsafe in adult seatbelts until they are 148cm tall.
"You can get some pretty tiny 7 year olds," said Mrs Rangi. "Some of our Kura kids are quite petite."
Masterton Shuttles provides a range of restraints as part of its service, and the Rangis are installing child safety harnesses, which can be tethered to the seat using anchor bolts.
"Parents will sometimes ask us, 'isn't it hard to keep carrying around car seats?"' she said.
"But with these new straps, we can just tuck them into the glove box until we need them."
Mr and Mrs Rangi say their insistence on using child restraints is, at times, met with raised eyebrows from other parents - but they are undeterred in their stance.
"I picked up one lady with a kid, and provided a booster seat - but the child didn't sit in it," said Mrs Rangi.
"Some parents might not see it as a positive thing. But, for me, I keep thinking about that storm we had. If that wind can flip a big truck on its side, imagine what it can do to a van full of kids.
"If the kids weren't in car seats, I'd hate to be the one on the side of the road ringing their parents, to say their precious 'taonga' have been in an accident."