The grievous assault on the baby boy led health officials yesterday to call for tougher regulations for childcare personnel.

Baby MJ Artwyutthikulwong sustained serious internal injuries and broken bones. He remains unconscious but in a stable condition at Bumrungrad Hospital's intensive care unit.

The nanny, Boonreung Katasarn, confessed to police on Monday evening that the child had slipped from her grasp and cried out loud. "In a rage, she battered him, causing his injuries," said Tao Poon police officer Lt Colonel Col Su-ek Chinthanasab.

"She'd been denying the charges [of assaulting and causing serious injury], but we had a medical record that proved the boy sustained his injuries from assault, not a bath-time accident. She confessed following a stressful interrogation," Su-ek said.

Police took Boonreung to re-enact the assault on Monday evening and plan to gather evidence for the public prosecutor to file a lawsuit against her.

Yesterday, after the interrogation was completed, Boonreung was taken to Ratchada Criminal Court, where her relatives placed a 5,200-square wah plot of land in Amnat Charoen province worth Bt520,000 as security for her release. The court had set bail at Bt120,000.

Meanwhile, the director of Ramathibodi Hospital's Child Safety Promotion and Injury Prevention Research Centre, urged the government to get tougher on the issuing of work permits for childcare personnel.

Dr Adisak Plitponkarnpim said baby MJ's injuries were unlikely to have been caused by an accident. Although babies his age still had a flexible skull and rib structures, the nature of his fractures and other injuries would have been caused by violent force. An accidental fall would not have caused such severe trauma.

Adisak also advised parents to choose nannies carefully from credible agencies and watch out for any suspicious changes in their child's behaviour. He urged the government to set stricter rules for childcare personnel, including tests on child-caring skills and their mental health.

Deputy Public Health Minister Morakot Kornkasem, who visited baby MJ yesterday, said there should be clear regulations for people in the childcare businesses and nannies.

The ministry would confer with related agencies such as the Education, Labour and Social Development and Human Security ministries to prevent such atrocities from recurring.

Some 800,000 new babies were born each year and 30 per cent were not under their parents' direct care, but looked after by others. Selecting child minders was an important issue, he said.

Meanwhile, Permanent Secretary for Social Development and Human Security Wanlop Phloytabtim said officials would check on the firm that employed Boonreung to see if it was legal and if they trained their personnel well enough. Officials would also contact MJ's parents to assist them with a lawsuit, as the assault breached the Child Protection Act.