Prospective memory (PM), the ability to initiate and implement delayed intentions, increases across childhood and adolescence. Previous evidence on older adults indicated beneficial effects of implementation intentions (an encoding strategy) on individuals’ PM performance; especially when cognitive control demands were high and availability of cognitive resources low. This research program set out to investigate the impact of implementation intentions on children's and adolescents’ PM while simultaneously varying cognitive control demands of the PM paradigm. Across two studies, implementation intention encoding was contrasted with standard encoding. In addition, Study 1 manipulated task importance (i.e., the strategic allocation of cognitive resources) and Study 2 switching demands of the ongoing task (i.e., the availability of cognitive resources). Overall 306 9-, 12- and 15-year-olds participated. Both studies revealed significant PM improvements from childhood to adolescence. Effects of task importance were reflected in PM reaction times but not in PM accuracy (Study 1). Participants showed longer reaction times when PM task importance was emphasized. Manipulations of switching demands of the ongoing task resulted in significantly increased PM accuracy and faster response times in the low- compared to the high-switching load task condition (Study 2). Neither Study 1 nor Study 2 showed beneficial effects of implementation intentions compared to simple PM instructions. Further, encoding condition did not interact with cognitive control conditions. Thus, findings of PM improvements following implementation intention encoding in older adults do not seem to extend to children and adolescents. Results are discussed in the light of current PM models.