A ban on child labour in Indian homes, restaurants and hotels goes into effect Tuesday but critics are already expressing doubts about whether it will be enforced.

Millions of children across the country work in roadside food stalls or in the homes of India's upper and middle class.

They also work by the millions in hazardous industries despite a nearly 20-year-old law that forbids children under 14 from working in industries such as fireworks, matchstick-making, auto workshops or carpet weaving.

The new ban also applies to children under the age of 14 and is supposed to protect youngsters from psychological and sexual abuse and overwork.

Social activists say that instead of legislation, more effort is needed to reduce the poverty that drives parents to push their children into dangerous jobs in the first place.

On Monday, Prime Minister Manmohan Singh threatened "firm action" against violators but also appealed to Indians to give up the practice voluntarily.

A conviction carries a penalty of up to two years in jail and a maximum fine of 20,000 rupees (about $500).

According to Reuters, the Labour Ministry says there are 12 million children under 14 years old working in India — the largest such group in the world — but activists say the number could be five times higher.

In an interview with the Hindustan Times, 12-year-old Sanjay, who cleans cars in a posh east Delhi colony, was unaware the law had come into effect.

Sanjay told the paper that he has been working for the past two years after his parents sent him to Delhi so that he could send money home to feed eight family members.

Child poverty experts with the United Nations said Tuesday that banning children from such work is just a first step. They urged Delhi to set up counselling support for freed children, provide shelters and ensure that they are welcomed back into their families.

"This declaration of political will needs to be concretized in the form of safety nets for the children who will be freed," Victoria Rialp, UNICEF's child protection chief in India, told Reuters.