Given the important limitations of direct (explicit) measures in psychological research with children, various scholars have focused on developing indirect (implicit) measures for different psychological constructs. However, children's well-being has traditionally been assessed in an explicit and direct way. For this reason, the first goal of the present research was to develop a new instrument to assess children's and adolescents' well-being using the Implicit Association Test (WB-IAT-Y). The second aim was to examine the relation between direct and indirect well-being measures. In this study, 358 primary and secondary school students answered the WB-IAT-Y, the Psychological Well-being Scales, and the World Health Organization - Five Well-Being Index. Finally, an expert conducted a semi-structured interview with each participant, asking about satisfaction with life in the main domains for children (i.e., family life, friends, school, and overall life satisfaction). The WB-IAT-Y showed good internal consistency and adequate construct validity. Factorial analyses indicated that this measure acted as an indirect measure. As in previous research, the WB-IAT-Y correlated weakly with the two well-being direct measures, and it showed the strongest correlation with the semi-structured interview conducted by an expert. To conclude, the new WB-IAT-Y instrument is a useful measure to assess indirect well-being for youths. We suggest that it is important to evaluate children's and adolescents' well-being using both direct and indirect measures in order to assess conscious and unconscious processing of self-relevant information.