Frequency and informativity of phonological input directed to children in the first four years of life

Information theory characterizes how signals are optimized for transmission from source to receiver across noisy channels, yet little is known about how these principles manifest when the receiver's capabilities change over time. Using child-directed speech as a natural experiment, we analyzed >7.5 million phones in North American English caregiver speech to children aged 3-44 months (N=218) from the CHILDES database. We found that while the relative frequency of individual phones remained stable over this developmental time period, phonological informativity increased from early infancy (3-8 months) through toddlerhood (27-32 months), before plateauing in the preschool years. This result suggests that speech directed to children sounds less redundant, with a phonological structure that is harder to predict in context, as children progress through early childhood. Our findings demonstrate how linguistic signals may be optimized to accommodate receiver (child) characteristics, with implications for both general principles of information transmission and theories of how children carve out linguistic representations and patterns from limited, noisy input.