Len Len Pedrero, 15, crawled her way round her last employers’ house in Manila, capital of the Philippines. She was so badly beaten she couldn’t stand, so she carried out her domestic chores on her hands and knees.

She said: “My whole body was in pain. I couldn’t walk any more. I would rather have died thansuffer there like an animal. I wanted to kill myself.”

Len Len managed to escape on her third attempt and now works as a live-in domestic for a better employer. She is not paid and still works very long hours in return for a roof over her head and food. But now her mother and sister live with her, too.

Others among the estimated one million child domestics in the Philippines are not so fortunate. One 14-year-old girl died last year after being forced to drink drain cleaner which burned her stomach. Some are tortured.

Child domestics make up more than a third of the estimated 250m child labourers around the globe - the largest but least visible group of working children.

Most are girls, some sold into domestic slavery at the age of five, and the majority are adolescents vulnerable to sexual assault and exploitation.

In the Indonesian capital, Jakarta, there are 700,000 domestic workers under the age of 18. In Venezuela, 60 per cent of working girls aged 10-14 are employed in domestic service. In West Africa, cross-border trafficking in such children is on the increase.

Such girls are the “silent Cinderellas” of the labour market, according to Maggie Black, co-author of the first international report on child domestic work just published by the United Nations Children’s Fund.

The report, Child Domestic Labour, concludes that lack of education is one of the worst deprivations such children suffer.

The report is part of an effort, led by Anti-Slavery International, to highlight the problem in advance of the final debate on the International Labour Organisation’s convention on child labour.