Background: Many children with specific language impairment (SLI) in sentence comprehension. These deficits are usually attributed to limitations in the children's understanding of syntax or the lexical items contained in the sentences. This study examines the role that extra-linguistic factors can play in these children's sentence comprehension. Aims: Extra-linguistic demands on sentence comprehension are manipulated directly by varying the nature of the materials used. Methods & Procedures Forty-five Italian-speaking children participated: 15 with SLI (mean age = 4;5), 15 typically developing children matched for age (TD-A, mean age = 4;5), and 15 younger typically developing children matched according to language comprehension test scores (TD-Y, mean age = 3;9). The children responded to sentence comprehension items that varied in their length and/or the number and type of foils that competed with the target picture. Outcomes & Results: The TD-A children were more accurate than the TD-Y children and the children with SLI, but, for all groups, accuracy declined when task demands increased. In particular, sentences containing superfluous adjectives (e.g., "Il topo bello copre l'uccello allegro"," "The nice mouse covers the happy bird" where all depicted mice were nice and all birds were happy) yielded higher scores than similar sentences in which each adjective had to be associated with the proper character (e.g., "Il cane giallo lava il maiale bianco", "The yellow dog washes the white pig", where foils included a yellow dog washing a pink pig, and a brown dog washing a white pig). Many errors reflected recency effects, probably influenced by the fact that adjectives modifying the object appear at the end of the sentence in Italian. Conclusions & Implications: Differences between conditions were observed even when lexical content, syntactic structure and sentence length were controlled. This finding suggests the need for great care when assessing children's comprehension of sentences. The same syntactic structure and lexical content can vary in difficulty depending on the number and types of foils used in combination with the target picture.