Understanding the impact of early-life nutritional choices on neurodevelopment in children is a growing area of research. To investigate the association between dietary patterns at multiple timelines and neurodevelopmental outcomes in 6-year-old children. This administrative observational study utilized a merged data from the national health insurance database and the health screening program for children. Information on the diet patterns from infancy to 3 years of age was obtained from parent-administered questionnaires. Dietary pattern clusters of the participants were identified using Polytomous Latent Class Analysis. The outcome was neurodevelopment using the Korean Developmental Screening Test (K-DST) at the age of 6 years. The study identified four distinct clusters among with the 133,243 eligible children (49.6% male, birth weight 3.22 kg, head circumference 42.7 cm at 4 months). The control cluster (53.4%) exhibited a diet including breast milk feeding and a variety of dietary patterns at the age of 1 year. In contrast, cluster 1 (36.0%) showed a skewed dietary pattern at the same age. Cluster 2 (6.6%) displayed diverse dietary patterns at one year but primarily consumed formula at four months, while cluster 3 (4.0%) had reduced dietary diversity and formula feeding. Compared with the control cluster, the adjusted odds ratio for unfavorable development was 1.209 (95% CI, 1.156-1.266) in cluster 1, 1.418 (95% CI, 1.312-1.532) in cluster 2, and 1.741 (95% CI, 1.593-1.903) in cluster 3. These findings remained consistent across individual domains of the K-DST. Dietary patterns during infancy and early childhood may be associated with neurodevelopment at the age of 6 years.