A new law in India bans children under 14 from working as domestic servants or on food stalls.
It also prevents children from working in teashops, restaurants, spas, hotels, resorts and other recreational centres.
PM Manmohan Singh has urged Indians to support his government's efforts to end child labour. People found breaking the law could face two years in prison.
India has more than 12.6 million child workers, many of whom are employed in the food and hospitality sector.
'Firm action'
In his appeal, on the eve of the law coming into force on Tuesday, Mr Singh said: "Our nation has solemnly pledged that children in our country are not engaged in any form of work at the cost of their right to education.
"As a major step in this direction, I call upon each one of you to stop employing children as workers and actively encourage children to join schools."
The prime minister warned that "the government will take firm action against those violating the law".
Officials say the ban on employing children in homes and roadside food stalls will affect 255,000 children.
But activists say these numbers could be as high as 20 million.
A senior official in the Labour Ministry, SK Srivastava, said: "The technical advisory committee on child labour regularly surveys the risk factors involved in any industry and depending on our findings we have taken this decision."
The committee, while recommending the ban, warned that children under 14 were vulnerable to physical, mental and even sexual abuse.
Laws 'ineffective'
Mr Srivastava said that anyone found violating the ban would be penalised under the Child Labour Prohibition and Regulation Act of 1986.
Punishment could range from a jail term of three months to two years and/or a fine of 10,000 to 20,000 rupees ($225 to $450).
But child rights activists are sceptical about the effectiveness of the ban.
They point out that although India bans the use of young workers in hazardous industries, thousands of children continue to work in firecracker and matchstick factories or are involved in carpet-weaving, embroidery or stitching footballs.
They say the laws have remained ineffective in curbing child labour.
Many parents say crippling poverty forces them to send their children, sometimes as young as five or six, to work in other people's homes or in factories.
Most of these children are made to work in unhealthy conditions for long hours and paid poorly.
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