Just six months old and lying defenceless in his mother's lap, a crying baby bore the brunt of his father's frustration when the man struck his head so hard, it caused multiple skull fractures.

This single act of violence in 2016 caused the child to suffer permanent disabilities, and he will require help with his daily functions for the rest of his life.

The boy is now two years and eight months old, but his developmental age is around four months old. He cannot sit, move, turn or flip over on his own. He also needs to be fed through a tube, the court heard.

The 30-year-old father, who works as a driver, pleaded guilty in court yesterday to causing grievous hurt to his biological son. He cannot be named due to a gag order to protect the boy's identity.

The incident occurred in the wee hours of Aug 26, 2016. The father of three was sleeping in his Bedok North flat when the boy's cries woke him up.

Deputy Public Prosecutor Grace Chua told District Judge Eddy Tham: "The accused shouted, 'Shut up la, shut up la. Later I have work, you make noise, I cannot sleep', and hit the victim once on the head with his right hand."

The man's 26-year-old wife held tightly onto their son, who began to cry even harder. A short while later, the baby vomited onto the floor before falling asleep. He appeared normal when he woke up at around 8am, but when his mother checked on him about five hours later, he was semi-conscious and weak.

The boy was taken to KK Women's and Children's Hospital in an ambulance. A CT scan of his head revealed that he had multiple skull fractures. He also had excess fluid in his brain and was immediately referred to neurosurgery doctors.

The baby was discharged on March 2 last year, about seven months after the incident. He is now living with his foster parents, who are receiving financial aid from the Ministry of Social and Family Development as well as the Singapore Enable Assistive Technology Fund.

DPP Chua said that to date, the boy has not recovered from his injuries. In June this year, his foster parents found that he was unable to move his limbs voluntarily.

In terms of speech, DPP Chua said the victim only coos.

"It is important to continue early intervention and close medical follow-up to prevent further complications.

"However, the victim is likely to continue to require assistance in all activities of daily living and mobility," she added.

Yesterday, DPP Kumaresan Gohulabalan, who was presenting the State's case with DPP Chua, urged the judge to sentence the man to at least 5 1/2 years' jail with six strokes of the cane.

He added: "When the victim was crying that day, instead of pacifying the victim or even checking on him to make sure that the victim was well, the accused betrayed the trust reposed in him by not only neglecting the victim, but also physically assaulting the victim."

Defence lawyer Shehzhadee Abdul Rahman, who was assigned to the case under the Criminal Legal Aid Scheme, pleaded for a four-year jail term with six strokes of the cane, adding that her client had assaulted his son during a momentary lapse of judgement. The man is expected to be sentenced today.