The development of numerical cognition is a critical foundation for children’s later mathematics performance, with number ordering as a key predictor of advanced competence. This study examines how children’s number ordering performance varies by number adjacency and size. A sample of 104 kindergartners arranged triplets of numbers in ascending order, with trials featuring adjacent or non-adjacent and small (1–10) or large numbers. Logistic regressions showed that adjacency, size, and their interaction significantly predicted performance, ps<.05. Children were more accurate with adjacent versus non-adjacent numbers and small versus large numbers. The interaction revealed the adjacency effect was driven by a higher accuracy on small adjacent versus non-adjacent numbers (p<.001); response accuracy was similar for large adjacent versus non-adjacent numbers (p=.27). These results, significant after controlling for verbal counting, ps<.001, underscore the importance of number adjacency and size in designing tasks to measure numerical skills.