TWENTY years ago, Yuen Chi-shing's mother sat him down with a babysitter, walked out the door and never came back. Today, after fruitlessly searching for his birth mother, Chi-shing is legally able to call the babysitter 'Mum' - thanks to an August 3 Family Court decision allowing him to be adopted. Mr Yuen, a Form Five graduate working in a bookshop, said: 'Although I do not know who my natural mother is, I am glad to have a mother now. 'I am grateful to her. She had no obligation to look after me; she was not paid but she brought me up and paid for my school fees. 'She is a great mother. I am lucky and proud to have her caring for me.' Twenty years ago, Mrs Yuen, 58, met a woman in a playground in Po On Road, Cheung Sha Wan, and was asked to look after a one-month-old boy without pay. The woman visited the child once or twice then disappeared. Mr Yuen told the Sunday Morning Post in April he knew nothing about this until the end of last year, when he needed a birth certificate to apply for a passport. 'I was shocked to hear that. I just could not believe it,' he said. A spokesman for the Social Welfare Department said the adoption order would be issued in two to three weeks. The family can then apply to the birth and death registration office for a formal certificate. The department has appealed for information about Mr Yuen's natural mother. It is known only that at the time she was 25, had short hair and was slightly overweight.