Various studies have demonstrated how the discrimination and violence experienced by LGBT+ children and young people affect their mental health and quality of life. Training for professionals working with children and young people is a key means of helping them provide the necessary support to LGBT+ children and youth people, for handling any violence that may occur in their immediate environment, as well as for empowering them. This article discusses changes in the attitudes, beliefs and practices of professionals working with children and young people following their participation in a Massive Open Online Course (MOOC) delivered through the online platform of the University of Girona. Two surveys were carried out with the participants -- the first at the beginning of the course, and the second at the end -- in order to evaluate possible changes. Participants' attitudes, beliefs and practices regarding sexuality and gender diversity in childhood improved, even when taking into account the fact that many began from an initial position of support. The use of MOOC training has value, given the need to engage with sexuality and gender diversity as part of formal training for a variety of professionals working with children and young people.