A maid smacked her employer's five-year-old son in a field in Punggol and deliberately threw him onto the ground twice when he struggled as she tried to carry him.

An eyewitness recorded a video of the incident with her mobile phone and posted the clip on a WeChat group earlier this year.

Deputy Public Prosecutor Ang Siok Chen said the video later went viral and was shared on Facebook as well as on citizen journalism site Stomp.

The 24-year-old Indonesian maid was yesterday sentenced to eight months' jail after pleading guilty to one count of ill-treating the boy.

She cannot be named as a gag order has been imposed to protect the boy's identity.

DPP Ang told District Judge Ng Peng Hong that the maid started working for the boy's family in November last year. Besides doing household chores, she was also required to look after the boy.

At around 9am on March 12, he took a ball, left his home and went towards the field in front of Block 673C Edgefield Plains.

The maid went after him and picked him up, the court heard.

The DPP said: "The victim struggled and the accused retaliated by smacking the victim's buttocks so that he would not struggle and fall off. The victim continued to struggle and the accused got frustrated.

"She then deliberately threw the victim onto the ground and carried (him) up again. As the victim continued to struggle, the accused purposely threw him down to the ground again."

After that, the maid carried the boy and took him home.

Later that day, he told his 34-year-old mother about the incident and complained about pain on his chest.

The maid denied ill-treating him and claimed that the boy had rolled on the ground on his own.

As a result, the mother did not pursue the matter.

But two days later, she came across the video on Facebook and learnt the truth. She made a police report and took her son to hospital, where he was found with mild tenderness over his spine.

For ill-treating the boy, the maid could have been jailed for up to four years and fined up to $4,000.