Development and validation of the NIH Baby Toolbox® language measures.

Language acquisition is a fundamental aspect of infancy and early childhood development. This paper describes the development and validation of the language measures within the NIH Baby Toolbox® (Baby Toolbox), a state-of-the-art assessment system designed for children aged 16 days to 42 months. The Baby Toolbox language domain includes six measures that assess both expressive and receptive language-Looking while Listening, Picture Vocabulary, CDI-CAT Comprehension, CDI-CAT Production, Mullen Receptive, and Mullen Expressive. These measures, offered in both English and Spanish, leverage advanced technologies-such as computerized adaptive testing and gaze-based paradigms-to enhance both the accuracy and accessibility of the assessment. A large-scale norming study (N = 2490 children; 2025 English-exposed, 465 Spanish-exposed) provided strong evidence of reliability and validity, with high test-retest correlations and robust construct validity, although small sample sizes prohibited analyses for some of the Spanish measures. Findings support the Baby Toolbox as a reliable, scalable tool for assessing early language development in diverse populations.