When presented simultaneously with equally discriminable, but unfamiliar, visual and auditory stimuli, 4-year-olds exhibited auditory dominance, processing only auditory information (Sloutsky & Napolitano, 2003). The current study examined factors underlying auditory dominance. In 6 experiments, 4-year-olds (N=181) were presented with auditory and visual compounds in which (a) the complexity and familiarity of stimuli were systematically varied (Experiments 1–5) and (b) participants were explicitly instructed to attend to a particular modality (Experiment 6). Results indicate that auditory dominance is a special case of flexible modality dominance, which may stem from automatic pulls on attention. Theoretical implications of these results for understanding the development of attention and cross-modal processing, as well as linguistic and conceptual development, are discussed.