A VOLUNTARY worker sexually molested four boys aged between seven and 14, the High Court heard yesterday. Metal shop worker Ng Kwok-yau threatened to beat up one of them and cut off the penis of another if the two boys refused to do as they were told, the court was told. Ng, 30, a voluntary worker for the Caritas Centre and the Henry G. Leong Yau Ma Tei Community Centre, pleaded guilty to five counts of indecent assault on a boy under 16. He also faced two other similar charges and one of attempted buggery that involved two different boys but the Crown decided not to proceed with these three counts. He will be sentenced by Mr Justice Leong on December 19, pending background and psychiatric reports. Counsel for the Crown, John Mullick, told the court the offences were committed between January 29, 1991, and June 7 this year on staircases or in corridors in Tsuen Wan buildings. In each case, Ng waylaid the victims, then indecently assaulted them. He also forced them to perform a sex act on him. One boy was attacked twice in six months. Ng threatened to beat up one of the boys and set fire to his home, if he told police what was happening. The youngest boy, aged seven, was told his penis would be cut off if he did not do as he was told. On July 4, the fourth victim and his mother were visiting Tsuen Wan Yan Chai Hospital. The boy saw Ng and recognised him as the man who had indecently assaulted him.