This study aims to investigate the extent to which language contact between Italian and Sicilian dialects has facilitated the integration of Differential Object Marking in the Sicilian regional variety of Italian, as compared to the Tuscan variety, which instead displays a limited use of a-marking of the direct object. The phenomenon was analyzed both in adult grammar and from a language acquisition perspective. Sicilian children’s behavior was directly compared to that of Tuscan children using the same topic elicitation task from Belletti and Manetti (2019). Additionally, an acceptability judgment task concerning DOM in various syntactic configurations (Topic, Focus, and SVO) was administered to two groups of Italian adults respectively from Tuscany and Sicily. Findings reveal a difference between the two regional varieties of Italian, evident both in adults’ and in children’s behavior. Specifically, in the Sicilian variety, a-marking does not notably help in resolving complex intervention configurations in featural Relativized Minimality terms (Friedmann, Belletti and Rizzi 2009), suggesting that DOM may already be integrated within the Case-agreement system. Conversely, in the Tuscan variety, prepositional marking appears limited to a-topics, being a peculiarity of left-peripheral Topic positions and helping to ameliorate intervention configurations when the direct object is dislocated in the highest part of the clause.