Incidents with the man hitting them with his hands, a toy fishing rod, plastic spoons and a leather belt were heard in the Whanganui District Court on Wednesday.
One of the children came home late from school one day after missing the bus, and was told by his siblings "Dad is going to give you a hiding," Judge David Cameron said.
"[The child] said that the defendant hit him with a force that would have been eight-and-a-half out of 10."
On another occasion the child accidentally broke a picture frame, and the man was about to hit him when the mother intervened, Judge Cameron said. However, when the mother went to the shops, the man hit the boy in the face, giving him a nosebleed.
In another incident, he hit the boy in the face when he locked the housekeys in the house, and accidentally broke a window trying to get in.
The man also hit other children, and kept them home from school so nobody would see the marks on their bodies.
In one incident the man threw one child against a wall and kicked them on the hip when they fell to the floor.
The boy described the kick as "five out of five - hard".
The man "then stood on [the child's] throat and held his foot down", Judge Cameron said.
The man denied this particular offending, but both Crown prosecutor Lance Rowe and defence lawyer Stephen Ross acknowledged no disputed facts hearing had been held, and it would not affect the end sentence.
Mr Ross said the man moved to New Zealand from Tonga when he was 17.
"The cultural context is raised because it is made clear in the probation report that [the defendant] still holds strong Tongan cultural beliefs," Mr Ross said.
He pointed out it was not until 2007 the law was changed to ban "reasonable" physical force when disciplining children.
Mr Rowe said the "key aggravating feature" of the sexual offending was "the extent of the breach of trust".
Mr Rowe also said the man knew the child assaults were wrong, despite his cultural beliefs, because he hid the children's injuries from other people.
Judge Cameron read from the mother's victim impact statement, where she described violence being part of their daily life: "She finds her anger against him hard to describe and she describes him as a violent man, hiding behind a quiet demeanour."
A pre-sentence report described the man as being at "moderate" risk of reoffending, and said he showed little remorse.
The man has no previous convictions, but as he committed multiple assault offences, Judge Cameron did not consider it appropriate to discount his sentence for that.
He sentenced him to two years and six months in prison and gave him a warning under the three strikes law.
