Bilingual children with a limited command of the second language (L2) often yield unsatisfactory results in L2-based non-word repetition tasks (NWRT) for the assessment of working memory. In this study, monolinguals (MO) and bilinguals (BI) of preschool age acquiring German were compared in regard to their performance on German-based NWRT to choose test items that do not put BI at a disadvantage. Four-year-old children (N = 876) were tested with the German language screenings "Sprachscreening für das Vorschulalter" (SSV) and "Kindersprachscreening" (KiSS), including 38 non-words. BI scored significantly lower in NWRT than MO due to a limited command of German as well as a limited language input (e.g., length of kindergarten attendance). After the statistical deletion of children who did not speak German age-appropriately, BI outperformed MO on the SSV, without significant differences on the KiSS. Performance on NWRT depended on the children's command of the German vocabulary and phonotactics. Several relatively "culture-fair" NWRT items were identified.