Code-switching, switching between different languages within the same conversation, is a prominent feature in bilingual communication. This study aimed to elucidate to what extent the linguistic abilities and age of dual-language-learning preschoolers influence the frequency and purposes of code-switching (compensatory, to bridge linguistic gaps; preferential, to express content as fluently as possible; pragmatic, to phrase something appropriately for the situation). Parental code-switching ratings of 101 German/French–Turkish/Italian dual-language learners aged 32–78 months were analyzed. Generalized linear mixed models revealed positive but no negative effects of societal- and heritage-language skills on children's code-switching frequencies independent of switching purposes and with no evidence of age effects. Hence, code-switching across the preschool age mainly reflects high linguistic competences. Models with linguistically and psychometrically parallelized language scores indicated a strong switching tendency toward the societal language when proficiency in both languages is high, and away from the societal language when language proficiencies are low.

Phonemic processing is largely influenced by how stimulus-specific characteristics of a language are computed, but person-level variables represent important moderators as well. The current study investigates how such characteristics, in parallel, affect receptive-level phonemic processing across the preschool age, and whether these effects are comparable across different languages. Using a child-friendly ‘odd-man-out’ discrimination task, we examined 239 monolingual German- and French-speaking preschoolers, aged three to five. Results revealed that phonotactic probability-based syllable frequency, nonword length, and mismatching nonword positioning effects explained independent variance components of phonemic processing. Age significantly affected how memory-related, but not linguistically relevant, stimulus characteristics were utilized for phonemic processing. Additionally, cross-language differences in rhythmic structure between German and French influenced which nonword segments received more attention focus. These findings provide novel insights into critical determinants of phonemic processing in preschoolers and highlight the need for further research to explore these effects over time and within varying language backgrounds.