In this longitudinal study on Finnish and Finnish-Russian families, infants’ play interaction at 7 months with each parent was observed during 5-minute play sessions ( N = 96) and predictive relations between co-regulated communication in mid-infancy and language development at 14 months were examined. Parental differences in communication were greater within the culturally diverse Finnish-Russian families than within the culturally less diverse Finnish families. Four family-level communication profiles were identified that differed with respect to how balanced, or similar, infants’ co-regulation with each parent appeared. Three of the profiles were equally distributed across the families, whereas one of the unbalanced profiles was typical for the culturally diverse families. Language exposure and balance of the family-level communication profiles in mid-infancy predicted differences in children’s expressive and productive vocabulary size beyond infancy.

Growth modeling was applied to monolingual (N ¼ 26) and bilingual (N ¼ 28) word learning from 14 to 36 months. Level and growth rate of vocabulary were lower for Finnish-Russian bilinguals than for Finnish monolinguals. Processing of Finnish speech sounds at 7 but not at 11 months predicted level, but not growth rate of vocabulary in both Finnish and Russian; this relationship was the same for monolinguals and bilinguals. The bilinguals' two vocabularies developed differently, showing no acceleration in Russian, the minority language. Even though the bilinguals progressed more slowly in each home language, they were learning at least as many new words as the monolinguals when Finnish and Russian vocabularies were counted together. Keywords bilingual first language acquisition, learning Finnish and Russian words, longitudinal study, speech perception in infancy, vocabulary growthDescribing the normative course of bilingual development has turned out to be a highly challenging task. It is still not well known how progression in learning two languages depends on age of acquisition, (dis)similarity and status of the language pairs, and context of exposure, as also recognized by Werker and ByersHeinlein (2008) and Bosch and Ramon-Casas (2014, this issue). Our goal was to examine early precursors to bilingual vocabulary growth; especially by examining how bilingual versus monolingual exposure from birth and speech perception in infancy relate to word learning in toddlerhood.

The study examines how dual‐ethnic and single‐ethnic families differ in terms of children's psychological adjustment and its correlates. Among 48 Finnish–Russian and Finnish families, mothers and fathers reported on children's emotional and conduct problems at ages 4 years and 7 years and children's emotion regulation, emotionality, and their own socialization values at 7 years. Mother–infant and father–infant coregulation was assessed at 7 months. The results show that children had more emotional problems among Finnish–Russian families than among Finnish families at 4 years but not at 7 years. Russian mothers reported more hierarchical and authoritarian values than did Finnish mothers, but the values did not moderate between ethnic context and children's adjustment. Equally many Finnish and Finnish–Russian families had balanced early coregulation, which was linked with fewer attention‐related problems at age 4. In both ethnic contexts, children's emotion regulation was concurrently associated with better psychological adjustment, and high emotionality was associated with more problems. Parental values were not associated with children's adjustment. Highlights This study from infancy to school age analyses psychological adjustment and its correlates among children growing up in single‐ and dual‐ethnic families. Parent‐infant unbalanced co‐regulation related with parent‐reported ADHD problems in preschool children who had more emotional problems in dual‐ethnic than single‐ethnic families. Found differences in parental values and emotion socialization did not expose children in dual‐ethnic families to enduring risk for problems in emotion regulation or adjustment.