Multisensory processing often results in facilitation and/or interference effects, yet the mechanisms remain unclear. The two reported experiments used a Stroop-like task to examine how congruent, incongruent, and irrelevant information presented in one sensory modality (e.g., visual) affects processing and responding in a different modality (e.g., auditory). Across two experiments, adults (E1) and 5-year-olds (E2) were presented with pictures and sounds, and they had to determine if what they saw or heard was an animal or vehicle. Experiment 1 with adults showed evidence of both facilitation on congruent trials and interference on incongruent trials, with unattended visual stimuli having a larger effect on auditory processing than vice versa. Results in 5-year-olds were slightly more symmetrical than adults but there was no evidence that auditory input dominated visual processing. Possible mechanisms underlying these effects are discussed.