Many studies have shown that bilingual children outperform monolinguals on tasks testing executive functioning, but other studies have not revealed any effect of bilingualism. In this study we compared three groups of bilingual children in the Netherlands, aged six-to-seven years, with a monolingual control group. We were specifically interested in testing whether the bilingual cognitive advantage is modulated by the sociolinguistic context of language use. All three bilingual groups were exposed to a minority language besides the nation’s dominant language (Dutch). Two bilingual groups were exposed to a regional language (Frisian, Limburgish), and a third bilingual group was exposed to a migrant language (Polish). All children participated in two working memory tasks (verbal, visuospatial) and two attention tasks (selective attention, interference suppression). Bilingual children outperformed monolinguals on selective attention. The cognitive effect of bilingualism was most clearly present in the Frisian-Dutch group and in a subgroup of migrant children who were relatively proficient in Polish. The effect was less robust in the Limburgish-Dutch sample. Investigation of the response patterns of the flanker test, testing interference suppression, suggested that bilingual children more often show an effect of response competition than the monolingual children, demonstrating that bilingual children attend to different aspects of the task than monolingual children. No bilingualism effects emerged for verbal and visuospatial working memory.

Recent research suggests that cognitive control plays a role in code-switching, both in bilingual adults and in bilingual children. Code-switching would only require cognitive control, however, when speakers maintain some degree of separation between their two languages, not when they completely mix the lexicons and grammars of their languages. For Frisian–Dutch bilinguals, mixing of Dutch (majority language) into Frisian (minority language) is common, but mixing of Frisian into Dutch is not. Therefore, Frisian–Dutch bilinguals need to maintain some degree of language separation when they speak Dutch, but not when they speak Frisian, predicting that code-switching from Dutch to Frisian would affect cognitive control more than vice versa. Frisian–Dutch bilingual children aged 5 and 6 (n = 104) completed a Flanker task. Information about frequency of code-switching from Dutch to Frisian and frequency of code-switching from Frisian to Dutch was obtained through a parental questionnaire. Multiple hierarchical regression analyses showed that frequency of code-switching from Dutch to Frisian significantly predicted performance on a Flanker task, but that frequency of code-switching from Frisian to Dutch did not. The results suggests that code-switching from Dutch to Frisian requires more cognitive control than code-switching from Frisian to Dutch. This is the first study that shows a code-switching asymmetry in the context of a minority–majority language pair. The study supports the hypothesis that code-switching requires more cognitive control when a bilingual speaker has to maintain some degree of language separation between her or his two languages.

This longitudinal study investigated to what extent the acquisition of cognates among bilingual children depends on the degree of cross-language similarity and intensity of exposure to the tested language, and whether children’s sensitivity to cognates with different degrees of cross-language similarity changes over time. For three consecutive years, 120 Frisian-Dutch bilingual children were tested on their Frisian receptive vocabulary. The sample was split into three groups that differed with respect to intensity of exposure to Frisian at home. In the receptive vocabulary task, cross-language similarity was systematically manipulated through four cognate categories, differing in their degree of overlap between Frisian and Dutch. The results showed a gradual cognate facilitation effect for children with a low intensity of exposure to Frisian. The higher the degree of cross-language similarity, the better their performance. This implies that the co-activation of the two languages depends on the degree of cross-language similarity. Over time, their performance improved the most on non-identical cognates with a cross-linguistic phonological regularity between Frisian and Dutch. This suggests that as they grow older, children with a low intensity of exposure to Frisian become better at recognizing regularities in the overlap of the Frisian and Dutch phonological systems.

Various studies have shown that bilingual children need a certain degree of proficiency in both languages before their bilingual experiences enhance their executive functioning (EF). In the current study, we investigated if degree of bilingualism in Frisian-Dutch children influenced EF and if this effect was sustained over a three-year period. To this end, longitudinal data were analyzed from 120 Frisian-Dutch bilingual children who were 5 or 6 years old at the first time of testing. EF was measured with two attention and two working memory tasks. Degree of bilingualism was defined as language balance based on receptive vocabulary and expressive morphology scores in both languages. In a context with a minority and a majority language, such as the Frisian-Dutch context, chances for becoming proficient in both languages are best for children who speak the minority language at home. Therefore, in a subsequent analysis, we examined whether minority language exposure predicted language balance and whether there was a relationship between minority language exposure and EF, mediated by language balance. The results showed that intensity of exposure to Frisian at home, mediated by language balance, had an impact on one of the attention tasks only. It predicted performance on this task at time 1, but not at time 2 and 3. This partially confirms previous evidence that the cognitive effects of bilingualism are moderated by degree of bilingualism and furthermore reveals that substantial minority language exposure at home indirectly affects bilingual children’s cognitive development, namely through mediation with degree of bilingualism. However, the findings also demonstrate that the effect of bilingualism on EF is limited and unstable.