Brain activation differences between 12 children (9- to 12-year-olds) and 12 adults (20- to 30-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI). Spatial selective attention was measured with the visual search for a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go no-go task. There were small developmental differences in the selective attention task, with children showing greater activation than adults in the anterior cingulate and thalamus. There were large developmental differences in the response inhibition task, with children showing greater activation than adults in a fronto-striatal network including middle cingulate, medial frontal gyrus, medial aspects of bilateral superior frontal gyrus, and the caudate nucleus on the left. Children also showed greater bilateral activation for the response inhibition task in posterior cingulate, thalamus and the hippocampo-amygdaloid region. The extensive developmental differences on the response inhibition task are consistent with the prolonged maturation of the fronto-striatal network.