CHILDREN as young as four are turning to crime because of the inadequacy of public assistance payments, social workers claimed yesterday. Community organiser of the Tsuen Wan Ecumenical Social Service Centre, Chan Yu, said she knew of cases involving children as young as four stealing, or threatening to steal, sweets and toys because their parents could not afford to buy them. Ms Chan added: ''The emergence of these criminal tendencies in children living on public assistance is quite shocking and highlights the need for the Government to substantially increase the child allowance.'' Many other children from families on public assistance have developed unsociable behaviour because their parents cannot afford to take them out or pay for extracurricular activities, she said. Welfare groups fear these children will never escape a life of poverty and will have difficulty finding work and forming relationships. A survey carried out by the Boys' and Girls' Clubs Association of Hong Kong on 17 families living on public assistance during October and November found that the average monthly payment for each family was $4,805 per month. Executive secretary of the association Mak Lok-sun said: ''The time has come for the Government to carry out a thorough assessment of the needs of these children and then raise the allowance accordingly.'' Welfare groups said the pressure on these families was particularly bad during Christmas and Lunar New Year when children were demanding gifts. Families whose income is too low to support their children or whose breadwinners cannot work because of the need to look after the children are entitled to public assistance, in which there is the child allowance component. In September, the plight of Hong Kong's 20,000 children on public assistance prompted 28 social and professional bodies to launch a campaign demanding higher allowances. In his policy speech in October, Governor Chris Patten pledged to increase the child allowance under the Comprehensive Social Security Assistance Scheme from $995 to $1,095 per month next April. But social welfare groups said this was nowhere near enough to cover the basic needs of these children and to ensure their proper social and educational development. Ms Chan said: ''1994 is the International Year of the Family and so we will be launching a big campaign to get society and the Government to look at the problems of low-income families.'' The association survey also found that 82 per cent of the families believe their children have learning difficulties, while half need personal tuition.