Gender stereotypes can harm children well being, impact on their career path an also led to discrimination behaviour. Our research aims at challenging children's gender stereotypes and exploring how a Digital StoryTelling tool can be be designed to detect these at early age. Based on the literature review we have developed a prototype named Genderalize that aims at stimulating children's reflection on their stereotypes. The tool was developed in a co-design process involving nine experts in children-computer interaction. The final version was tested by nine the adults stakeholders (e.g. guardians, parents, teachers). The outcomes provide thoughtful considerations on how Genderalize helped the detection of gender stereotypes by the means of a contextualised narrative and the reflective exercises. Results' impact was limited due to the small sample, but the outcomes were very useful to move on to the next step of the project and inspire new developments.