Child witnesses often describe their experiences across multiple interviews. It is unknown whether talking with a familiar interviewer increases disclosures, however, or whether any benefits of a familiar interviewer could be achieved by ensuring that interviewers (regardless of familiarity) behave in socially supportive ways. This study tested the effects of interviewer familiarity and social support on children's reports of an adult's transgressions.We predicted that familiarity and supportiveness would increase transgression reports at a second interview and that children who spoke with familiar, supportive interviewers would disclose the most transgressions.Children (N = 160, 5 to 9 years) participated in a science event involving 6 transgressions. Across 2 interviews, they spoke with the same trained university student interviewer or different interviewers, and these interviewers engaged in supportive or neutral behaviors. Interviews were coded for overall information reported, number of transgressions, and confabulations.There were no effects of support in the first interview or on total details reported in either interview. Children reported more transgressions to supportive than neutral interviewers in the second interview (IRR = 1.19), even during open-ended prompting (IRR = 1.26), and they omitted fewer transgressions that had been reported in the first interview (IRR = 0.69). Confabulations were infrequent. There were no condition differences in the total number of confabulations reported across interviews, but these errors occurred more often in the second interview in the supportive condition.Interviewer support may play a greater role than familiarity in facilitating children's testimony. (PsycINFO Database Record (c) 2019 APA, all rights reserved).