Internal state language (ISL) research contains knowledge gaps, including dimensionality and predictors of growth, addressed here in a two-aim study. Parent-reported expressive language from N = 6,373 monolingual, English-speaking toddlers (Mage = 23.5mos, 46% male, 57% white) was collected using cross-sectional and longitudinal data in WordBank. Exploratory and confirmatory factor analyses suggested a best-fitting one-factor model of ISL. The single-factor model of ISL was then submitted to hierarchical linear modeling to evaluate predictors of ISL development. Age 2 ISL production was predicted by child sex, wherein females outperform males, and maternal education, wherein higher education contributes to higher ISL. Only maternal education emerged as a significant predictor of ISL growth. These results provide support to theory suggesting a unitary construct of ISL, as opposed to considering ISL as categorical, and further illustrate linear growth through the second postnatal year that varies as a function of child sex and maternal education.

Mental State Talk (MST) is utterances describing invisible mental aspects. The first aim of this study was to investigate the characteristics of Parental MST and Child MST and their concurrent association in a Swedish population, and the second aim was to relate these MST measures to the children’s general language abilities. Seventy-seven dyads of parents and their 25-month-old toddlers participated. MST was assessed by videotaping the dyads during free-play sessions in a laboratory and general language abilities were based on parental reports. Forty-nine toddlers did not produce MST, while all parents used MST. Child MST was positively associated with vocabulary and grammar. Parental MST was not associated with Child MST nor the children’s general language abilities. In exploratory analyses, Parental MST referred to another than the child was positively correlated with vocabulary and grammar. Further studies are needed to confirm these findings and continue studying MST in different linguistic contexts.

The present study explored developmental differences in preschoolers’ use of reported speech and internal state language in personal narratives. Three-, four-, and five-year-olds attending a laboratory preschool shared 204 stories about ‘a time when you were happy/sad’. Stories were audio-recorded, transcribed, and coded for reported speech (direct, indirect, narrativized) and internal state language (cognitive states, total emotion terms, unique emotion terms). Personal narratives told by five-year-olds included more cognitive states and more narrativized speech than those told by three- and four-year-olds, even when accounting for children’s vocabulary skills, and that reported speech (narrativized, direct) were positively correlated with cognitive state talk. These findings highlight distinct shifts in children’s use of cognitive state talk and reported speech in personal narratives told at age five. Associations between reported speech and internal state language are both informed by and support Vygotsky’s (1978) fundamental claim that psychological processes are socially mediated by language.