JAKARTA (Reuters) - The authorities in the sprawling Indonesian capital are cracking down on the exploitation of children after a raft of cases, from child labour to violence and sexual assault, was uncovered in recent weeks.

Tens of thousands of children are trafficked annually in Indonesia, with the majority forced into prostitution and manual labour, the United Nations' child welfare agency Unicef says.

The drive follows the arrests last month of several Jakarta residents who sedated infants and used them to beg for money or hired them to motorists looking to evade minimum passenger norms designed to fight the city's notorious traffic congestion.

"These cases are a wake-up call for us all to improve our policing style, to make it proactive and prevent violence against children," said Jakarta police spokesman Mohammad Iqbal.

The authorities have begun designating safe houses for vulnerable children in the city, besides tightening patrols in neighbourhoods where there are many children, he added.

This week, the city government suspended a rule requiring each car to carry at least three passengers, saying it was encouraging child labour.

The measure had been aimed at congestion in Jakarta, where poor public transport forces commuters to spend three or four hours in their cars each day, at an annual cost to the economy of about 65 trillion rupiah (S$6.6 billion).

The practice of hiring extra passengers, or "jockeys", off the street to satisfy the three-passenger rule has long been in use in the city of 10 million people.

But the discovery of some jockeys drugging babies and offering them for hire prompted authorities to suspend the rule.

"Many victims are traumatised and stressed when they come to us, so we have to counsel them," said Mr Neneng Heryani, the director of a state-run rehabilitation centre that offers academic, sport and musical activities for the children.

The centre in East Jakarta looks after about 40 children, but thousands more remain at risk of exploitation.

Experts have welcomed the latest efforts to combat child abuse, but have urged the government to take a comprehensive approach in tackling the problem.

"At the moment this is more like firefighting and reactionary," said Mr Arist Merdeka Sirait, chief of a national panel on child protection, pointing to an urgent need for preventive measures.

"People need to be educated," he said. "The whole mindset needs to be changed, to think of children not just as a source of income, but as needing protection."