Languages differ in the preferences for the interpretation of the scope relation between negation and a quantifier. This study investigates the understudied issue of how interpretive preferences associated with a quantifier scope in learners’ L1 and L2 affect their scope interpretations in L3 acquisition. Based on the current models of L3 acquisition, we tested which language, L1 or L2, exerts a stronger effect on the L3 acquisition of quantifier scope. To this end, the study involved two groups of multilingual children (11–13 years old) with different L1s (Chinese or Russian) but with the same L2 (Korean) and L3 (English). The participants completed truth-value judgment tasks designed to investigate their interpretation patterns for English sentences with negation and a quantifier (e.g., Tom did not cut all the trees). The results showed that both groups preferred the L3 interpretation similar to that preferred in their L2, but not in their L1, suggesting a potential L2 influence on L3 acquisition. The study evaluates L3 acquisition theories in light of these results.