Abstract: Background：Constructing language development milestones and collecting milestone data are not only key steps in language development monitoring, but also the preliminary basis for the development of language screening and diagnostic tools. Objective：To construct language development milestones for Chinese-speaking children aged 0 to 5.5 years, providing a reference basis for language development screening and diagnostic tool development. Design：Cross-sectional survey. Methods：Based on existing developmental assessment tools and literature, a language development milestone item pool was established through expert consultation and cognitive interviews. From October 2022 to November 2022, 1,976 children aged 0 to 6 years were sampled from five provinces including Zhejiang, Sichuan, Liaoning, Jiangxi, and Hainan. Using stratification by urban and rural areas, gender, and age groups, developmental milestone data were collected through parent reports in both primary care settings (age <36 months) and kindergartens (age ≥36 months). The characteristics of language development milestones for children in different age groups were analysed descriptively using an item response theory model. Data comparisons were conducted between the data collected in the current study for Chinese-speaking children and data obtained from other published research on English-speaking children. Main outcome measures：Response rate, different item function, model fit, and estimated developmental age of each item when passing probabilities is 25%, 50%, and 75%. Results：A total of 63 language development milestone items were included in the item pool. After data cleaning, 1 659 children were included in the data analysis, including 827 boys and 832 girls, with an average age of (2.5±1.9) years. The response rate for all 63 language milestones was higher than 99%. Three items showed different item function based on maternal education, and 14 items showed poor model fit. Conclusions：The language development milestones for Chinese-speaking children aged 0 to 5.5 years established using the item response theory model provide a clear description of the language development trajectory of native Chinese-speaking children. This work offers valuable empirical data for the future development of language development evaluation tools for Chinese-speaking children, clinical monitoring of language development, and research into related neural mechanisms.

Key words: Children, Language Development, Milestones