BackgroundStudies on perinatal risk factors and the developmental delay of children have been inconclusive and few studies have assessed the association between infants and toddlers’ body mass index (BMI) and developmental outcomes.MethodsWe conducted a cross-sectional study of children aged 1—36 months who had a routine physical examination in the child health departments of hospitals from March 2018 to November 2021 in 16 provinces, 4 autonomous regions and 2 municipalities directly under the central government by using the Infant Toddler Growth Development Screening Test (ITGDST). Normal children were defined as those with scores ≥ mean – 2 standard deviations (SD), while children with developmental delay were those with scores < mean—2SD in terms of overall development, gross motor, fine motor and language development. Binary logistic regression was used to analyze the risk factors of gross motor, fine motor, language and overall neurodevelopment.ResultsAfter removing some provinces with a small sample size and children with incomplete data, 178,235 children with 12 complete variables were included in the final analysis. The rate of overall developmental delay was 4.5%, while 12.5% of children had at least one developmental delay aspect. Boys, parity, advanced maternal age, multiple birth, cesarean section, neonatal injury, family heredity history, microcephaly, abnormal BMI at birth and at physical examination after controlling the confounding of other factors had a significant effect on development delay (overall neurodevelopment, gross motor, fine motor or language development). Per capita gross domestic product was a protective factor for the children’s neuropsychological development.ConclusionsThis study reveals significant associations of perinatal factors and BMI with developmental delay in the Chinese children aged 1–36 months, which may be crucial for early intervention.