Artificial Intelligence (AI) and Machine Learning (ML) have heavily irrupted in society, bringing new applications and possibilities while introducing some ethical problems. Governments and institutions around the world are working on the challenges posed by AI in all aspects, from economy to education. Therefore, introducing AI-related content at school and exploring how this kind of content can be taught becomes mandatory. In this paper we carry out a bibliographic revision of previous works done on ML, and then describe an educational resource developed by the institution of the first two authors (INTEF) aimed to teach ML in schools with Scratch and Machine Learning for Kids. The testimonials of three educators, who have implemented their own version of these resources, are depicted. More efforts should be made to introduce AI-related content in education.