Understanding complex sentences that contain multiple clauses referring to events in the world and the relations between them is an important development in children's language learning. A number of theoretical positions have suggested that factors like syntactic structure (clause order), iconicity (whether the order of clauses reflects the order of events), and givenness (whether information is shared between speakers) affect ease of comprehension. We tested these accounts by investigating how these factors interact in British English-speaking children's comprehension of complex sentences with adverbial clauses (after, before, because, if), while controlling for language level, working memory and inhibitory control. 92 children in three age groups (4, 5 and 8 years) and 17 adults completed a picture selection task. Participants heard an initial context sentence, followed by a two-clause sentence which varied in: (1) the order of the main and subordinate clause; (2) the order of given and new information; and (3) whether the given information occurred in the main or subordinate clause. Accuracy and response times were measured. Our results showed that given-before-new improves comprehension for four- and five-year-olds, but only when the given information is in the initial subordinate clause (e.g., “Sue crawls on the floor. Before she crawls on the floor, she hops up and down”). Temporal adverbials (after, before) were processed faster than causal adverbials (because, if). These effects were not found for the eight-year-olds, whose performance was more similar to that of the adults. Providing a context sentence also improved performance compared to presenting the test sentences in isolation. We conclude that existing accounts based on either ease of processing or information structure cannot fully account for these findings, and suggest a more integrated explanation which reflects children's developing language and literacy skills.