This study examined the developmental trajectories of Arabic grammatical number in Arabic-English bilingual children. The samples consisted of 80 individuals (40 monolingual children residing in Jordan and 40 bilingual children residing in the USA), aged between 5 and 9 years. Data was collected through two tasks involving picture able objects and naturally occurring communications. Although bilingual children's accuracy in plural processing demonstrated an age-related improvement, the findings reported a notable delay in plural form acquisition within the bilingual age-related trajectories. Transparency, frequency, and productivity contributed to shape the acquisition patterns of plural form among 5-7-years-old children, while predictability becomes a salient factor for the older trajectories. The study also highlighted the productivity of bilingual children to employ the feminine sound plural (FSP) as a default mechanism in generating diverse plural nouns. Prominent strategies in producing plural forms by bilingual children encompassed over-generalization of the FSP, code-switching between plural patterns, and utilization of the English plural morpheme [-s] and English quantifiers. The study, therefore, concludes that children predominantly adopt a single route mechanism during the processing of the inflectional system. Finally, the study offers noteworthy pedagogical implications pertinent to the instruction of Arabic-English bilingual children.