Objective: The measurement of Family Feedback on Child Welfare Services (FF-CWS) is gaining prominence as an efficacy indicator and is coherent with concerns about family-centered practice and empowerment. The aim of this study was to develop and validate an instrument that would overcome the scarcity of psychometrically sound measures in this field. Methods: Following item construction and selection, exploratory and confirmatory factor analyses with a sample of 263 Spanish (52%) and Portuguese (48%) caregivers of children involved with CWS were conducted. Results: Three subscales were identified: Intervention Efficacy, Perception of Workers, and Satisfaction with the Intervention Process. In general, all dimensions showed good reliability, convergent, and criterion-related validity results. Multigroup analyses confirmed measurement invariance for both countries. Conclusions: The FF-CWS Questionnaire is a brief self-report measure that can be a useful assessment tool to frontline practitioners, agency managers, and policy makers for program evaluation and planning.