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.