The MacArthur-Bates Communicative Development Inventories (CDIs) are widely used parent-report tools for assessing early language development, including gesture use, expressive and receptive vocabulary, and early morpho-syntactic capacities. While originally developed for typically developing children aged 8 up to 36 months and aimed at detecting developmental language disorder, CDIs have been increasingly applied in studies of neurodevelopmental and genetic conditions, where language development often diverges from typical trajectories. In this review, we synthesize literature on the use of CDIs in a range of clinical populations, including autism, Down syndrome, Williams syndrome, cerebral palsy, Angelman syndrome, DDX3X syndrome, 5p deletion syndrome, fragile X syndrome, and others. We highlight condition-specific patterns of expressive vocabulary development, discuss the value of longitudinal data collection using CDIs, and visualize age trends that capture change and variability across developmental pathways. Particular attention is given to methodological considerations such as cross-linguistic adaptations, reporting biases, and the limitations of single-timepoint assessments. While CDIs show promise for tracking language trajectories and informing early support, challenges remain in ensuring their reliability, validity, and suitability as screening tools. We conclude by emphasizing the importance of longitudinal, cross-condition, and cross-cultural approaches to better understand atypical language development and to improve the utility of CDIs in both research and applied settings.