Studies on the processing of non-active (NACT) voice have indicated that passive sentences are more difficult to comprehend and require more time to process. Children with Reading Difficulties (RDs) face problems with sentence comprehension, which are often attributed to phonological processing, working memory, syntactic awareness limitations, or a maturation delay. Using an online self-paced reading task, we investigated the effect of voice morphology and argument structure on sentence processing in 3 groups of participants; 30 children RDs, 28 Age-Matched (AM) controls without RDs, and 28 young Beginning Readers (BRs). Our results suggest that although the RDs and BR groups present similar reading times, their reading patterns differ qualitatively. Beginning Readers experienced greater processing delays when processing NACT structures, suggesting that they have not yet fully grasped the properties of the various NACT verbs. However, the RDs group presents effects not found in the BR group; children with RDs were sensitive to the properties of the different types of NACT verbs showing (a) evidence that the language processor successfully engages in predictions based on the morphosyntactic and lexical characteristics of verbs and (b) preference for default/prototypical readings. These results point toward processing limitations that are greatly affected by syntactic complexity.