A woman who worked as a nanny for the three children killed in Timaru has described them as an "awesome family" with "wonderful kids" and no obvious problems. 

Twin 2-year-old girls Maya and Karla and their 6-year-old sister Liane (police said they had earlier given incorrect ages for the girls) were yesterday named as the dead children. 

Police yesterday arrested and charged a 40-year-old woman with murder in relation to the deaths. The woman is due to appear in the Timaru District Court this morning. A scene examination will continue at the Queen St address today. 

Mandy Sibanyoni worked as a childminder for the Dickasons in South Africa. 

Both parents "loved their kids like nobody's business," she said. 

"I'm torn apart, a part of mine is gone," Sibanyoni said in an interview with The Associated Press in Pretoria. "And it's like those kids, they are my kids too because I raised them." 

"I don't know what to do about this because the only question that I've got now is, what happened? What went wrong?" 

She told TimesLIVE: "I never saw any fight in that family or anything. We treated each other as family. I was family too. There was nothing wrong." 

Sibanyoni said "they were such nice children". 

"They listened when you told them not to do that, and when they wanted something they would ask. We used to play outside and take a walk on the streets. When I come in they used to be excited that Mandy is here. They would say goodbye to their mother and 'we are going to play with Mandy'," she told TimesLIVE. 

"Now I am shattered. I am not coping." 

The children and their parents had only recently arrived in Timaru from their native South Africa, having relocated to start a new life here. 

On arrival to New Zealand they completed the mandatory MIQ period. Days later, the ultimate tragedy unfolded. 

Nothing on the mother's social media pages over recent months when she was living in Pretoria, South Africa, indicated anything was amiss. 

She posted pictures of her family and of bakery treats, and wrote about the virus, urging people to get vaccinated. In May, she marked the couple's wedding anniversary on Facebook. 

"Happy 15th wedding anniversary ... What an adventure. We have truly created a beautiful family and had many good times together," she wrote. "May the next years be more blessed, more happy and may the kids let us sleep." 

Inspector Dave Gaskin, the Aoraki area commander, said the deaths were "incredibly distressing" for residents of Timaru, particularly after five teenagers from the town were killed in a car crash last month.