Bilingual advantages in memory flexibility, indexed using a memory generalization task, have been reported (Brito & Barr, 2012; 2014), and the present study examines what factors may influence memory performance. The first experiment examines the role of language similarity; bilingual 18-month-old infants exposed to two similar languages (Spanish–Catalan) or two more different (English–Spanish) languages were tested on a memory generalization task and compared to monolingual 18-month-olds. The second experiment compares performance by trilingual 18-month-olds to monolingual and bilingual infants’ performance from the first experiment. The bilingual advantage in memory flexibility was robust; both bilingual groups outperformed the monolingual groups, with no significant differences between bilingual groups. Interestingly, an advantage was not found for infants exposed to three languages. These findings demonstrate early emerging differences in memory flexibility, and have important implications for our understanding of how early environmental variations shape the trajectory of memory development.