Pediatric advance care planning (ACP), which aims to ensure care is aligned with family goals and values, is associated with better end-of-life outcomes; however, ACP in pediatrics remains uncommon. To determine the feasibility and acceptability of the Pediatric Serious Illness Communication Program (PediSICP) and explore family-centered outcomes. This cohort study was a single-group pilot study of the PediSICP in adolescents and young adults (AYAs; age ≥13 y) with serious illness, parents of seriously ill children, and interprofessional clinicians from April 2021 to March 2023 in a quaternary care pediatric hospital. Duration of follow-up was 1 month. Data were analyzed from January 2022 to March 2023. The PediSICP includes clinician training preceding an ACP communication occasion supported by communication guides and a template for electronic medical record documentation. Outcomes of interest were parent, patient, and clinician experiences with and perceptions of the PediSICP. Feasibility was defined a priori as at least 70% clinician intervention completion rates. A total of 10 virtual trainings were conducted among 40 clinicians, including 27 physicians, 7 nurse practitioners, 5 nurses, and 1 respiratory therapist, and 30 trained clinicians (75%) conducted and documented 42 ACP conversations with 33 parents (median [IQR] age, 43 [35-51] years; 25 [76%] female) and 5 AYAs (median [IQR] age, 19 [17-19] years; 3 [60%] female) who completed the intervention. The median (IQR) conversation duration was 27 (10-45) minutes. Most clinicians (29 clinicians [97%]) agreed that they felt prepared for the conversation, and all clinicians recommended the PediSICP. Parents reported participation was worthwhile (27 parents [84%]), they felt listened to (31 parents [94%]), and would recommend the PediSICP (28 parents [85%]). Parents endorsed higher therapeutic alliance after the PediSICP intervention compared with before (The Human Connection scale mean [SD] score, 57.6 [6.4] vs 55.3 [7.8]; P = .03) and decreased anxiety immediately after the intervention (Generalized Anxiety Disorder-7-item mean [SD] score, 10.1 [7.3] vs 8.4 [6.9]; P = .003), which persisted at the 1-month follow-up (mean [SD] score, 7.7 [6.8]; P = .03). This pilot cohort study found that the PediSICP was feasible, acceptable, and highly valued by clinicians and parents of children with serious illness. These findings suggest that the PediSICP may empower interprofessional clinicians and improve ACP with families of children and AYAs who are seriously ill.