In this study, we investigated how Mandarin-speaking children and adults interpret focus structures like Zhiyou Yuehan chi-le pingguo Only John ate an apple and Shi Yuehan chi-de pingguo It is John who ate an apple. We found that children tended to associate focus operators zhiyou only and shi be with the verb phrase (VP), whereas adults uniquely associated them with the subject noun phrase (NP). To account for this difference, we propose that children initially treat focus operators as adverbials, thus ending up associating them with the VP. In order to assess our proposal, we examined children's understanding of zhiyou-constructions with negation, like Zhiyou Yuehan meiyou chi pingguo Only John didn't eat an apple. It was found that children, like adults, consistently associated the focus operator with the subject NP in this construction. The findings have an important bearing on language learnability, since negation assists children in reaching the adult-like interpretation.