The present article provides an overview of some recent research in bilingual first language acquisition with special reference to Romance languages. It addresses two language contact phenomena, language mixing at the lexical level and crosslinguistic influence at the syntactic level. For both contact phenomena, there is evidence that they are unrelated to language dominance (as measured in terms of MLU). Language mixing is negatively correlated with the number of utterances per minute, a measure for language fluency. Cross-linguistic influence at the syntactic level is due to computational complexity which is caused for example by the invasive interplay of pragmatics and syntax. This kind of interplay will be discussed on the basis of the presence or absence of the null-subject property, comparing Italian and German, and by studying the presence or absence of object clitics, comparing French and German. Since cross-linguistic influence affects bilingual individuals to different degrees (sometimes referred to as individual variation), the assumption is discusseds that the degree to which the influence manifests itself differs as a function of fluency (measured in words produced per minute). The more fluent the child is in the language with the computationally complex analysis, the less the effect of cross-linguistic influence. In sum, the language which exhibits influence is determined by computational complexity as defined, for example, by the invasive interplay between pragmatics and syntax. The degree of manifestation of the influence depends on fluency in the computationally complex language.