High- profile child murders lead parents to fear for their children's safety, but perception of risk is often at variance with reality. We explore the numbers of potential 'Extra- familial' child homicide assailants in the United Kingdom and estimate their actual murder rate to determine risk levels. A south of England study, equivalent to a 4 per cent sample of the UK population, of a decade of consecutive child homicides identified the characteristics of child homicides assailants, finding that the most frequent assailants- the 'intra- familial' - were very different from 'Extra- Familial' assailants. 'Extra- familial' killers were all males, aged nineteen to forty- two, with convictions for violent- Multi- Criminal- Child- Sex- Abuse (MCCSA) offences and Multi- Criminal- Child- Sex- Abuse (MCCSA), whose victims were aged seven- plus years. Projecting these characteristics onto the male UK population enables us to estimate the numbers of potential UK 'Extra- Familial' assailants, which are set against known UK child (five to fourteen) homicides (WHO, 2005). To account for any 'hidden' child homicides, deaths in the 'undetermined' violent death category, designed 'Other External Cause' (OEC), are calculated to provide a 'maximum' child homicide rate. There were potentially 912 VMCCSA and 886 MCCSA 'Extra- familial' offenders in the United Kingdom, who could be responsible for the WHO- reported UK three- year average of 'Extra- family' fifteen child homicide and seventeen OEC deaths per annum; a homicide rate of 12, 061 per million (pm) for VMCCA and 3, 386 pm for MCSA, which is 1.21 and 0.34 per cent; however, the VMCCSA homicides rate was 403 times greater than the all children accident and cancer death rates. Though the vast majority of these potential assailants did not kill, comparatively, they are extremely dangerous. Practice and ethical issues are debated, which considers active outreach for the 'treatable' to possible 'reviewable' custodial sentences for the VMCCSA.