Different inflectional endings of masculine animate and inanimate nouns in the accusative are common to Croatian and Russian and constitute Differential Object Marking (henceforth DOM) in these two languages. Additionally, Russian nouns of all genders get DOM in the plural, making this feature even more consistent. In this paper we investigate the acquisition of DOM by Russian and Croatian children. Our longitudinal data reveal that in both languages DOM is acquired early. However, the acquisition route is different. While Croatian children erroneously extend the use of the Acc=Gen to inanimate forms, Russian children start with erroneously 0-marked animate forms and switch to erroneously overmarked (Acc=Gen) forms much later.