The study examined the acquisition of two morphological procedures of noun pluralization in Palestinian Arabic: "Sound Feminine Plural" (SFP) and "Broken Plural" (BP). We tested if noun pluralization was affected by (1) the type of morphological procedure, (2) the degree of familiarity with the singular noun stem, and (3) the frequency of plural patterns. Thirty-six native Arabic-speaking children in three age groups were tested on three experimental tasks: a repetition task, a structured production task, and a seminatural production task. In line with earlier research, the results showed that SFP pluralization was acquired earlier and had a shorter developmental trajectory than BP plurals. Also, the errors of children showed that SFP was a dominant default procedure. However, despite its early consolidation, SFP formation was affected by familiarity with the singular noun stem. BP nouns also appeared rather early in the production of children and were affected by both familiarity with the noun stem and frequency of the plural pattern. Yet, they took longer to acquire and did not reach comparable levels to SFP in the age groups tested. The implications of the results for models of language acquisition and the acquisition of Arabic morphology are discussed. (Contains 7 tables and 7 figures.)