Background: Inferior vena cava (IVC) ultrasound measurement is a reliable indicator used in the assessment of intravascular volume status. The aim of this study was to evaluate intravascular volume changes in pediatric patients by measuring the IVC diameter and collapsibility index (CI) in children whose oral feeding was restricted preoperatively. Material and Methods: From May 2018 to October 2018, a total of 55 pediatric patients who were scheduled for surgery were included in this prospective, observational, cohort study. Fasting and satiety IVC diameters and CIs of patients were determined by ultrasonographic evaluation twice: in the preoperative preliminary evaluation, when the patients were satiated, and before surgery, during a fasting period of 6–8 hours. Ultrasonographic data were recorded and compared between fasting and satiety periods. Results: In the grey scale (B-mode), mean IVC diameter was significantly higher when the patients were satiated, compared to the measurements made just before surgery during the fasting period. In the M mode, the mean IVC diameter was significantly higher only during the inspiratory phase when the patients were satiated, while during the expiratory phase it was detected to be statistically similar. Mean CI was significantly higher in the immediate preoperative period, compared to the assessment made when satiated. Conclusion: Preoperative ultrasound IVC diameter and CI measurement can be a practical and useful method for evaluating preoperative intravascular volume in children.