Defence lawyers have questioned the credibility of a young Hong Kong boy who had testified against his parents and step-grandmother over abuse he suffered and the death of his five-year-old sister.

The eight-year-old “told lies and exaggerated things”, the boy’s class teacher wrote in a WhatsApp conversation with a social worker that was read out in court by defence counsel Chase Pun, acting for the grandparent on trial over child cruelty inflicted upon the two children.

“Yes, that’s right,” the teacher testified on Wednesday.

“And this comment reflects the truth,” Pun continued.

When the teacher did not immediately reply, the counsel added: “Otherwise, you won’t tell the social worker as such, is that right?”

“That’s my instinct,” the witness replied.

Public prosecutor Justin Ma Yu-kit then asked: “What do you mean by instinct?”

The teacher – whom the Post is not naming due to a gag order aimed at protecting the identities of the children – replied that he had that feeling because there were discrepancies in the accounts of the child and his stepmother sometimes.

“The information provided by [the boy] was not entirely true and correct,” he added.

That dishonesty and a failure to submit homework on time were said to be the reasons the child was suspended from duty as a class monitor when he was in Primary Three, the year he was abused and the matter came to light.

“So you believed the stepmother?” the prosecutor asked.

But before the witness could answer, he was interrupted by Mr Justice Albert Wong Sung-hau, who observed: “Does that go too far into collateral issues? He found inconsistencies, that’s all. It’s only a judgment of the witness himself.”

The judge added that he was not barring the question. Ma, however, withdrew it and sat down.

The High Court previously heard the boy recount years of abuse, which included being hit by his father, stepmother and step-grandmother. The child also said his father had tossed his five-year-old sister at the ceiling 18 times the night before she died on January 6, 2018, while his stepmother was said to have watched and initiated another “game” which involved swinging the child back and forth.

The children’s 29-year-old father and 30-year-old stepmother have admitted to child cruelty, inflicted over a period of 150 days from August 10, 2017, when they relocated to reside with their 56-year-old step-grandmother, but denied murdering the girl.

The grandmother has denied all four counts of the cruelty charge.

None of the defendants or their relatives can be identified due to the gag order.

Senior assistant director of public prosecutions Derek Lai Kim-wah had accused the parents of taking “all measures” to ensure others did not get to see the children’s injuries – such as removing them from school and telling “a pack of lies” to the teachers and social worker who noticed.

The teacher confirmed that the boy was absent for 20 out of 81 school days from the start of his Primary Three academic year in September 2017, up from just two days in the two previous years.

When asked why the child was made a class monitor, the teacher replied: “He was a pretty good kid in class, constantly willing to help others.”

The witness was also the teacher who noticed the child had a swollen face and difficulty walking at school on November 6, 2017. The following day, the teacher noticed various other injuries and beating marks.

The injuries included bruises below the boy’s left eye and both sides of his face, tenderness on his upper lip, abrasions on his right elbow and scar on his left wrist.

On November 8, the school notified the child’s paternal grandmother, who used to take care of him. But the boy was picked up by his stepmother before the grandmother reached the school, and he did not show up in the next two days.

Worried about his safety, the grandmother and her two other sons visited the school to make inquiries on November 10. But the teachers did not disclose the family address, and instead suggested they make a police report. A report was then lodged at Tuen Mun Police Station.

On the same day, the father applied for his son’s sick leave and asked the school not to contact his mother again.

In court, the teacher said the school fulfilled that request after the father explained that his relationship with his mother was not very good.

He also confirmed that the school did receive a doctor’s sick leave certificate, explaining that the child was suffering from an eye inflammation on November 9 and 10.

The boy was last seen at school on December 19, 2017.

The jury trial continues on Thursday.