Polish and Ukrainian pattern together syntactically in allowing various omissions in the same discourse settings, for example, when the referring element has been mentioned in a previous context. However, Ukrainian employs full object pronouns morphologically, whereas Polish uses clitics in the same environments. We exploit this contrast to compare the acquisition of clitics versus full pronouns, enriching previous accounts of omissions in child speech. The results of an elicited production experiment reveal that, in the two languages considered, 3- to 6-year-old children make no errors in direct object realization, but prefer to use null arguments up to the age of 5. It is crucial that there is no obvious difference between the acquisition patterns for clitics versus pronouns, which suggests that the morphophonological properties of direct objects are not primary predictors of object realization in languages that allow discourse-related omissions.