Two of the sexual violation charges were added today after further evidence from one alleged victims. Kupa has pleaded not guilty to the charges.
Opening the Crown case today, prosecutor David Stevens said CYF placed many children with Kupa, but he physically assaulted six of them - with the youngest a boy of five or six at the time - by kicking them, pulling their ears, hitting them, including with a foam bat, and getting other children to hit them. Kupa also allegedly drenched one of the girls in her bed with a fire hose and made her sleep in the wet bed.
While having a fast food takeaway meal, Kupa made the "naughty kids'' eat grass sandwiches and gave them a plate of stones rather than food.
"He told them not to tell anybody as 'what happens in the home stays in the home','' Mr Stevens said.
Two of the girls, aged 14 and 15, were sexually abused, including rape, sodomy and other sexual violations, including while the two girls were in a tent on the front lawn of the Whangarei CYF home, the court heard.
Mr Stevens said Kupa told the girls he wanted to show them "how men and women do things".
The mother of one of the alleged sexual abuse victims broke into sobbing in the back of the court while Mr Stevens outlined the case and she had to be helped out of the courtroom.
Mr Stevens said the law allowed a parent or guardian to use reasonable physical force when disciplining children, but Kupa's abuse went well beyond that, while there can be no defence of consent in relation to the sex offences.
The children were placed in Kupa's care because they were considered vulnerable by CYF and that for whatever reason, their families could not care for them at that time.
Mr Stevens said the assault charges were representative, meaning the children were assaulted at least once, and the Crown had to prove the charges beyond reasonable doubt.
Defence lawyer Kelly Ellis said Kupa's defence was that the alleged physical assaults were actually him using reasonable force, as allowed under law, and had been exaggerated by the children.
"The defence case is that these sexual acts simply did not occur. This is a story that just keeps growing,'' Ms Ellis said.
The trial before Justice Raynor Asher and an eight-woman, four-man jury is set to last least nine days.