Abstract Background Many patients diagnosed with a serious illness have significant relationships with children (< 18 years old). While effective communication about an adult’s illness has psychological benefits for children, many families are uncertain about how to approach this topic. Patients frequently seek guidance from healthcare professionals, but clinicians often report a lack of knowledge, skills, and confidence to initiate such conversations. Consequently these discussions are often avoided. A novel, brief intervention has been created to overcome these well-documented barriers. This multimethod study aimed to evaluate the acceptability, usefulness and effectiveness of an intervention for healthcare professionals. Methods Volunteer sampling was used to identify and recruit healthcare professionals working with adult patients who have a serious illness. Participants completed an online survey regarding their current clinical practice, knowledge, skills and confidence about family-centred conversations before immediately accessing the intervention. Participants were invited to complete the same survey after accessing the intervention and give brief feedback about its usefulness. A subset of participants were contacted three months after their engagement with the intervention to participate in an online, individual interview. Non-parametric Wilcoxon signed-rank tests were conducted to evaluate differences between pre-post survey scores. Interviews were transcribed and analysed using reflexive thematic analysis. Results Two hundred and fifty-five healthcare professionals completed the survey pre-post intervention. Quantitative responses indicated that the intervention had significantly increased participants’ knowledge, skills and confidence to initiate family-centred conversations. Over 90% reported that the intervention was relevant to their practice and 88% agreed they would recommend it to a colleague. Qualitative results (n=16) are discussed under three themes 1) perceptions of the intervention 2) perceived impact of the intervention on clinical practice 3) opportunities and challenges for family-centred conversations in routine practice. Participants commented favourably on the tone, format and content, with many describing a change in their practice. Conclusions Healthcare professionals reported an increase in their knowledge, skills and confidence to initiate family-centred conversations after engaging with the intervention. Further evaluation is required to assess the sustainability of reported behaviour-change by healthcare professionals and its impact on patient and family outcomes.