This paper investigates early productions of children learning German and Spanish in both monolingual and bilingual conditions. The monolingual cross-linguistic findings reveal quantitative differences in truncation and different ways of overcoming size restriction and acquiring complex words, that are accounted for within Optimality Theory, by means of two different constraint hierarchies. The emergence of these different grammars is important for the analysis of bilinguals' complex prosodic structures and the relationships between their two phonological modules. The outcome of the interaction of the two languages is mainly attributed to markedness.