This report is intended as a source of information to be used in the development and evaluation of child safety restraints. It is in the main literature survey of Australian, British and American sources. It demonstrates that a suitable characteristic which may be used to accurately define a restraint size is the child’s mass. It provides dimensions for relevant body lengths, such that 98 per cent of children of a given mass will be comfortably restrained. In order to have the means of testing the size of the restraint, designs are produced for four body blocks of mass, 9, 14, 19 and 38 kilograms.