This study investigated the referring expressions used for first mentions of participants and entities in narratives by Mandarin heritage language (HL) and monolingual children. Referring expressions for first mentions in Mandarin comprise lexical, morphological and syntactic devices. Results showed that HL children used less adequate referring expressions for first mentions than the monolinguals, mainly due to overgeneralization of classifiers and lack of vocabulary knowledge. However, HL children did not differ from monolinguals in their use of relative clauses and post-verbal NP placement to mark first mentions. These results suggest that incomplete acquisition of the HL may vary across different linguistic subdomains (Montrul, 2008); specifically, domains requiring a great deal of input to acquire, such as vocabulary and the large repertoire of classifier morphemes, might be more vulnerable in HL speakers than syntax. Mixed modeling analyses revealed that older age of arrival, higher maternal education levels and a rich and diverse Mandarin environment at home predicted stronger narrative outcomes, also pointing to an important role for input in HL acquisition.