This paper compares the language of child bilinguals and adult unbalanced bilinguals (heritage speakers) against that of bilingual native speakers of their home language (baseline). We identify four major vectors of correspondence across the language spoken by these three groups. First, all varieties may represent a given linguistic property in a similar way (child bilinguals = adult heritage speakers = bilingual native speakers of their home language). This occurs when either (i) the property in question is highly robust and is acquired by learners without difficulty or (ii) the property is already in decline in the baseline. We illustrate scenario (i) with data from Russian count forms, which are morphologically quite complex. The preservation of these forms in child bilinguals and adult heritage speakers suggests that simplicity of encoding is not the only factor determining robustness of retention. Second, child and heritage speakers may share a linguistic structure that differs from the one found in the baseline (bilingual native speakers of their home language = child bilinguals = adult heritage speakers). This scenario occurs when incipient structural changes in the baseline become amplified in the language of next-generation bilinguals, or when a given structure is rare, confined to a specific register, and/or reinforced through literacy. Third, a structure may be acquired by bilingual children faithfully, but undergo reanalysis/attrition in the adult heritage language (bilingual native speakers of their home language = child bilinguals = adult heritage speakers). Russian relativization illustrates this scenario; child bilinguals show native-like performance on relative clauses but adult heritage speakers show an exaggerated subject preference in the interpretation of gaps. Finally, a structure that is not fully learned by child speakers may be reanalyzed by adult heritage speakers following general principles, thus bringing the adult heritage representation closer to that of the baseline (bilingual native speakers of their home language = adult heritage speakers = child bilinguals). Heritage speakers’ production and comprehension of psychological predicates in Spanish illustrates this possibility.