Biases in the processing of emotional facial expression have been the subject of much debate in the literature. Opposing views on this topic claim either that positive or negative facial expressions enjoy improved processing capabilities in the human brain. This disagreement may stem from examining different participant ages, and the use of various testing paradigms. Thus, the resulting findings may reflect differing aspects of facial emotion processing and therefore lead to differing results. To investigate the specific aspect of how rapidly an observer can access emotional valence information from a facial stimulus depending on the observer’s age and the original stimulus valence, we investigated different children’s age groups compared to adults with the same emotion categorization task in a single study. Six-, 9-, and 12-year-old children, as well as adults were asked to categorize various facial expressions as positive or negative as quickly as possible. Our results show an early age processing advantage for positive faces, which disappears in adults who show no such differences in the case of response time measures. In the case of accuracy measures, the early advantage for positive faces gradually disappears, and is in fact reversed into a negativity advantage in adults. These findings demonstrate that positive and negative processing advantages are strongly modulated by age, and can vary even within a single testing methodology depending on the developmental stage of the participant.