Objective: The objective of this study was to audit current patient blood management practice in children throughout cardiac surgery and paediatric intensive care unit (PICU) admission. Design: This was a prospective observational cohort study. Setting: This was a single-centre study in the cardiac operating room (OR) and PICU in a major tertiary children's hospital in Australia. Patients: Children undergoing corrective cardiac surgery and requiring admission to PICU for postoperative recovery were included in the study. Measurements and main results: Fifty-six patients and 1779 blood sampling episodes were audited over a 7-month period. The median age was 9 months (interquartile range [IQR] = 1–102), with the majority (n = 30 [54%]) younger than 12 months. The median number of blood sampling episodes per patient per day was 6.6 (IQR = 5.8–8.0) in total, with a median of 5.0 (IQR = 4.0–7.5) episodes in the OR and 5.0 (IQR = 3.4–6.2) episodes per day throughout PICU admission. The most common reason for blood tests across both OR and PICU settings was arterial blood gas analysis (total median = 86%, IQR = 79–96). The overall median blood sampling volume per kg of bodyweight, patient, and day was 0.63 mL (IQR = 0.20–1.14) in total. Median blood loss for each patient was 3.5 mL/kg per patient per day (IQR = 1.7–5.6) with negligible amounts in the OR and a median of 3.6 mL/kg (IQR = 1.7–5.7) in the PICU. The median Cell Saver® transfusion volume was 9.9 mL/kg per patient per day (IQR = 4.0–19.1) in the OR. The overall median volume of other infusion products (albumin 4%, albumin 20%, packed red blood cells) received by each patient was 20.1 mL/kg (IQR = 10.7–36.4) per day. Sampling events and blood loss were positively associated with PICU stay. Conclusions: Patient blood management practices observed in this study largely conform to National Blood Authority guidelines. Further implementation projects and research are needed to accelerate implementation of known effective blood conservation strategies within paediatric critical care environments.