Child Vocabulary and Developmental Growth in Executive Functions During Toddlerhood.

Executive functions (EFs) emerge in the first years of life and are essential for many areas of child development. However, intraindividual developmental trajectories of EF during toddlerhood and their associations with ongoing development of language skills remain poorly understood. The present three-wave study examined these trajectories and their associations with language skills. Child EF and vocabulary were assessed around 13, 19, and 28 months of age in a sample of 145 toddlers (51% boys) from mostly White families. At each time point, mothers reported on child receptive and expressive vocabulary, and EF were assessed with three behavioral tasks targeting inhibitory control, cognitive flexibility, and working memory. Multilevel growth models revealed that toddlerhood is a period of significant developmental growth in child inhibitory control, cognitive flexibility, and working memory. The findings also provide evidence for a sustained relation between toddlers' language skills and their ongoing acquisition of inhibitory control and cognitive flexibility. This study offers novel insight into intraindividual developmental changes in EF during toddlerhood and the role of language in these meaningful, though neglected, changes.