The ability to attend to one among multiple sources of information is central to everyday functioning. Just as central is the ability to switch attention among competing inputs as the task at hand changes. Such processes develop surprisingly slowly, such that even into adolescence, we remain slower and more error prone at switching among tasks compared to young adults. The amplitude of oscillations in the alpha band (~8–14 Hz) tracks the top‐down deployment of attention, and there is growing evidence that alpha can act as a suppressive mechanism to bias attention away from distracting sensory input. Moreover, the amplitude of alpha has also been shown to be sensitive to the demands of switching tasks. To understand the neural basis of protracted development of these executive functions, we recorded high‐density electrophysiology from school‐aged children (8–12 years), adolescents (13–17), and young adults (18–34) as they performed a cued inter‐sensory selective attention task. The youngest participants showed increased susceptibility to distracting inputs that was especially evident when switching tasks. Concordantly, they showed weaker and delayed onset of alpha modulation compared to the older groups. Thus the flexible and efficient deployment of alpha to bias competition among attentional sets remains underdeveloped in school‐aged children. The amplitude of alpha band oscillations (~10Hz) modulates as a function of selective attention. These modulatory effects are considered to reflect attentional regulation of sensory information processing. Here we tested the developmental trajectory of these processes in a cued cross‐sensory selective attention design in participants ranging in age from 8 to 34 years of age. Cross‐sensory attention related alpha modulation in the cue‐target interval was present even in the youngest participants, whereas age differences were reflected in greater behavioral costs as well as reduced switch‐specific alpha modulation in the youngest group on trials in which the participant was cued to switch between attended sensory modalities. These data suggest that the ability to fully bring these attentional processes online is still developing in childhood, with implications for more attentionally taxing situations.