Bilingualism has sometimes been associated with cognitive boosts, particularly in working memory (WM). However, it remains unclear whether such benefits extend to the comprehension of syntactically complex structures. We investigated this through a gamified character-selection task assessing comprehension of subject-relative clauses and object-relative clauses among monolingual ( n = 31) and bilingual ( n = 28) French-speaking children, as well as monolingual ( n = 45) and bilingual ( n = 43) German-speaking children aged 3 to 12. We examined whether comprehension correlated with verbal WM, measured through a nonword repetition task, and interference resolution ability, assessed through a Simon task and an analysis of comprehension errors. The results indicated no bilingual advantage: object-relative clauses were more difficult than subject-relative clauses across all groups and languages. While interference-related errors — misinterpreting object-relative clauses as subject-relative clauses more frequently than vice versa — surfaced in all groups, verbal WM correlated with object-relative comprehension only in French. These findings are discussed in relation to current theories of bilingualism and WM in language comprehension.