PARTICIPA Erasmus+ project proposes a multilevel professional development approach targeting early childhood education (ECE) professionals in Portugal, Belgium, Poland, Greece, through the development of a toolkit supporting participatory practices. PARTICIPA aims to strengthen ECE professionals’ knowledge, skills, and positive attitudes towards children’s participation. Children’s right to participate in ECE, essential to a democratic society, is an indicator of ECE quality, and ECE professionals are crucial to its promotion (Sheridan, 2007). Children have the right to participate in all matters affecting them, freely expressing their views and having them considered (United Nations, 1989). However, the implementation of this right remains a challenge to ECE professionals. Thus, it is important to support professionals’ knowledge, attitudes, and practices towards children’s participation. The project involves the development of three independent but complementary tools (massive open online course and two self-assessment tools), using a mixed methods approach. Focus groups with professionals were already conducted, to inform design/content of the tools (currently being finalized). A feasibility study relying on self-report and observation measures (currently under preparation) will examine their iterative development.PARTICIPA will require the approval of the coordinating Institution Ethical Committee, and comply with data protection requirements (e.g., professionals’ consent; anonymized information). We will present PARTICIPA project and its main goals: a minimum of 1000 ECE professionals using the toolkit (final version), increasing their knowledge, positive attitudes, and competences in designing, implementing, and monitoring participation practices. We expect long-term improvements in ECE classroom/centre quality; children’s wellbeing; respect for children’s views; ECE organization/functioning; perceived procedural justice.