A man who pushed his girlfriend's one-year-old son off a bed with so much force that the baby broke his skull was yesterday sentenced to 6 1/2 years' jail and six strokes of the cane.

The infant had bleeding in his brain but miraculously survived the ordeal on March 25 last year - after emergency surgery. Now aged three, the boy is in foster care and undergoing rehabilitative therapy.

His tormentor, Franklie Tan Guang Wei, 26, pleaded guilty earlier this month to one charge of causing grievous hurt and three out of four charges of ill-treating a child.

District Judge Hamidah Ibrahim said a deterrent sentence was needed to signal society's disapproval and reprobation of Tan's conduct.

"The most glaring and obvious aggravating factor is the fact that these acts of abuse were committed against a defenceless and vulnerable child... His only crime was the fact that he cried, a natural thing for him to do at his age, and could not be consoled, which (Tan) found frustrating," she said.

The boy was born in mid-2013, after his father lost contact with his mother, who is now 25. In August 2014, she got into a relationship with Tan, who did odd jobs and last worked at a mobile phone shop. The next month, the infant's behaviour changed.

"(He) appeared to be fearful of males and started having nightmares in his sleep," Assistant Public Prosecutor Dillon Kok said.

Two nannies who looked after him also found bruises on his body.

"When (the mother) was questioned, she denied that (he) had been abused and claimed that there were 'spirits' in the flat," Mr Kok added.

In November 2014, the mother got pregnant with Tan's child and moved in with Tan and his mother.

On Nov 8, the baby's cries woke the couple. Tan slapped him once, leaving finger marks on his cheek and bruising near his ear.

Three days after the incident, a nanny took photos of the bruises and swelling. She made a police report about the injuries on Nov 19 and the Child Protective Service was informed. The baby was then put under the nannies' care, and the mother and Tan were allowed only weekly supervised access. Tan's grandparents later took over from the nannies in taking care of the baby in February last year, with the couple granted supervised access again.

But on March 8 last year, Tan's grandfather left the infant at Tan's flat. That night, frustrated with his cries, Tan threw the baby at his mother, who was about 2m away. The infant fell against her body.

Later, Tan and the mother were allowed to spend the nights with him. But on the morning of March 25, angered by the baby's cries, Tan hit his buttocks twice, causing a bruise.

After the mother went to work, leaving the infant alone with Tan, the baby vomited on the bed. Angry, Tan forcefully pushed him off the bed with his right arm.

The infant landed face-up on the floor about 2m away and vomited. Tan took him to the toilet to shower but did not check the water temperature first, scalding his upper back.

Later, Tan noticed that the baby was in a daze and semi-conscious. He was also vomiting repeatedly. Tan told the mother, who went home to find the infant weak and very pale. They took him to hospital.

The mother has been charged with two counts of permitting Tan to ill-treat the baby. Her trial is scheduled to begin next Monday.

Defence lawyer Gino Hardial Singh submitted a psychiatric report that said Tan has persistent depressive disorder, poor emotion regulation and low intelligence.

Tan could have been jailed for up to 10 years, fined and caned for causing grievous hurt. For child abuse, he could have been fined $4,000 and jailed for four years per charge.