SummaryHigh 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 UK and estimate their actual murder rate to determine risk levels.A South of England study, equivalent to a 4% sample of the UK population, of a decade of consecutive child homicides identified the characteristics of child homicide assailants, finding that the most frequent assailants, the `Intrafamilial', were very different from `Extra-familial' assailants. `Extra-familial' killers were all males, aged 19-42, with convictions for Violent-Multi-CriminalChild-Sex-Abuse (VMCCSA) offences and Multi-Criminal-Child-Sex-Abuse[MCCSA], whose victims were aged 7plus 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 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.