The storing of dry-assembled and primed extracorporeal membrane oxygenation (ECMO) circuits is common practice and endorsed by the Extracorporeal Life Support Organization (ELSO) for up to 30 days. We conducted an anonymous survey among chief perfusionists in German neonatal and pediatric ECMO centers to identify key parameters of the actual clinical practices. Ten of 15 (67%) participating centers do not pre-assemble and pre-prime circuits in apprehension of future patients. The average storing times in 33% of the centers exceed the ELSO recommended 30 days up to 150 days. Longer storing times may be the result of less annual cases compared with adult ECMO. The addition of concentrated erythrocytes in the priming fluid may be one reason for ad-hoc de-airing. None of the participating centers treats children exclusively, omitting the center’s overall experience as reason for the different practices in adults and children. Nonetheless, the average time required for assembly and de-airing was extended by 40% compared with adult ECMO while the perceived urgency in emergency situations was increased. Overall, this study shows distinct differences between adult and neonatal/pediatric ECMO regarding circuit preassembly and prepriming that indicate the need for improved standard operating procedures and specific research.