Background: Globally, the problem of hidden harms to children of parents who use drugs and alcohol has been recognized. However, it is at a community level that resources must be allocated.

Objective: The aim of this research was to provide a methodological framework for estimating the prevalence of children with potential hidden harms, in a community setting.

Methodology: Benchmark–multiplier methods were used. Alcohol dependency was measured using the Rapid Alcohol Problem Screen tool. A retrospective audit of records combined with a multisource enumeration to remove duplicates was used to derive a minimum benchmark and a multiplier for the number of children to known adults. Further benchmarks were derived from the localized data of a general population survey. Community services were consulted for estimate validation, needs, and recommendations. The setting was an Irish urban disadvantaged region in 2016.

Results: From the audit and multisource enumeration, a ratio of 0.88 children to every one client known to local treatment services was estimated. This provided a minimum estimate of 3.7% of children at risk of being impacted by illicit drug use where parents were known to services. From the general population survey and the local multiplier, an estimate of 15–24% of children potentially impacted by illicit drug use was derived. Finally, from the alcohol dependency data, an estimate of 14–37% of children possibly impacted by parental alcohol dependency was derived.

Conclusions: Estimates were accepted as realistic by service providers who highlighted the need to improve interagency and interdisciplinary communication between drug and family services.