The present article investigates the acquisition of the pronominal systems by French and Italian monolingual children and by bilingual German-French and German-Italian children, demonstrating a stable asymmetry: object and reflexive clitics are acquired later than nominative clitics and strong subject and object pronouns. We will widen the scope of former investigations to include the acquisition of strong pronouns and argue that the observed asymmetry can be accounted for if we combine the external (categorial status) and internal syntax of pronouns (internal structure). In particular, we argue for the relevance of the absence/presence of a nominal layer (N-layer) in the internal structure of a pronoun. This approach can account for the observation that pronouns containing an N-layer, i.e., strong subject pronouns, subject clitics and strong object pronouns, are acquired simultaneously and earlier than pronouns which lack the N-layer, i.e., object clitics and reflexive clitics.