Children have a right to Comprehensive Sexuality Education (CSE). A key place for this to occur is in schools, and teachers’ comfort and competence in teaching is critical to delivering high-quality CSE. Good quality Initial Teacher Education (ITE) should provide student teachers with a strong foundation for the delivery of CSE and the creation of safe, supportive, and inclusive classrooms and whole-school cultures. This study examined primary ITE students’ perceptions of the quality of input, knowledge and confidence, and attitudes towards Relationships and Sexuality Education (RSE). The study was conducted in Ireland where RSE is mandatory in the primary school curriculum. The level of input student teachers received in RSE was perceived to be insufficient, and less than that provided in other curricular areas. Student teachers reported moderate to high levels of perceived knowledge and comfort in RSE domains and high levels of commitment and intention to teach RSE once qualified. They overwhelmingly agreed that children and young people have the right to RSE. Student teachers reported being particularly unprepared to teach RSE to students with special educational needs and sexual and gender minority students. Recommendations are made for strengthening RSE input in ITE programmes.