Non-invasive and comprehensive assessment of aortic conduit and reservoir function based on 4D flow MRI is feasible and has potential clinical relevance in congenital vascular conditions such as hypoplastic left heart syndrome (HLHS) in infants. The reservoir function depends on the mechanical compliance of the vessel wall and confers the ability to respond to flow and pressure changes. Its assessment is based on the pulse wave velocity (PWV), frequently obtained from skin tonometry sensors or imaging studies. The conduit function of the aorta is assessed by the pressure differences along the vessel, with larger differences indicating higher resistance to the flow and hence a worse conduit function. PWV between aortic root and mid lower thoracic descending aorta, as well as variations in diameter and elastic module, can be estimated from temporally sparse but spatially dense velocity vectors available from 4D flow MRI in diagnosed infants. In this context, one-dimensional (1D) hemodynamic flow simulations can assimilate in vivo measurements and reveal vascular properties of conduit and reservoir function. In this work, we investigate on the modeling decisions and their implications when working with the challenging MRI data acquired in children with HLHS. Our goal is to provide robust and accurate vascular biomarkers by 1D patient-specific models of the aorta hemodynamics in infants, i.e., models that recapitulate the observed velocity field while minimizing discrepancies with the fundamental physical principles.