Bilingual children often experience difficulties with inflectional morphology. The aim ofthis longitudinal study was to investigate how regularity of inflection in combination with verbalshort-term and working memory (VSTM, VWM) influences bilingual children’s performance. Datafrom 231 typically developing five- to eight-year-old children were analyzed: Dutch monolingualchildren (N= 45), Frisian-Dutch bilingual children (N= 106), Turkish-Dutch bilingual children(N= 31), Tarifit-Dutch bilingual children (N= 38) and Arabic-Dutch bilingual children (N= 11).Inflection was measured with an expressive morphology task. VSTM and VWM were measured witha Forward and Backward Digit Span task, respectively. The results showed that, overall, childrenperformed more accurately at regular than irregular forms, with the smallest gap between regularsand irregulars for monolinguals. Furthermore, this gap was smaller for older children and childrenwho scored better on a non-verbal intelligence measure. In bilingual children, higher accuracy atusing (irregular) inflection was predicted by a smaller cross-linguistic distance, a larger amount ofDutch at home, and a higher level of parental education. Finally, children with better VSTM, but notVWM, were more accurate at using regular and irregular inflection.