Proactive interference (PI) occurs when previously learned memories compete with currently relevant information. Despite extensive literature investigating the effect in adults, little work has been done in young children. In three preregistered studies (N = 38, 35, 172; convenience samples from the Northeastern United States), first, we showed that 3-year-old toddlers are highly sensitive to the effect of PI in visual working memory and second, that these effects can originate from the reactivation of previously encoded information. Third, we tested how the ability to cope with PI changes between 2.5 and 7.5 years of age. Besides providing an estimate for the size of the interference effect at the youngest age to date, our findings have an important methodological implication: paradigms that repeat items across trials potentially underestimate young children's working memory abilities.