Background: The aim of this prospective, age‐stratified, observational study was to determine the cranial extent of spread of a large volume (1.5 ml·kg^?1, ropivacaine 0.2%), single‐shot caudal epidural injection using real‐time ultrasonography. Methods: Fifty ASA I‐III children were included in the study, stratified in three age groups; neonates, infants (1–12 months), and toddlers (1–4 years). The caudal blocks were performed during ultrasonographic observation of the spread of local anesthetic (LA) in the epidural space. Results: A significant inverse relationship was found between age, weight, and height, and the maximal cranial level reached by 1.5 ml·kg^?1 of LA. In neonates, 93% of the blocks reached a cranial level of ≥Th12 vs 73% and 25% in infants and toddlers, respectively. Based on our data, a predictive equation of segmental spread was generated: Dose (ml/spinal segment) = 0.1539·(BW in kg)–0.0937. Conclusions: This study found an inverse relationship between age, weight, and height and the number of segments covered by a caudal injection of 1.5 ml·kg^?1 of ropivacaine 0.2% in children 0–4 years of age. However, the cranial spread of local anesthetics within the spinal canal as assessed by immediate ultrasound visualization was found to be in poor agreement with previously published predictive equations that are based on actual cutaneous dermatomal testing.