At the closure of the UNESCO decade on Education for Sustainable Development (2005-2014), this article reports on large research projects on sustainability conducted within the World Organisation for Early Childhood Education (OMEP) through 2009-2014. The overall aim of the projects within OMEP was to enhance awareness of Education for Sustainable Development among young children, OMEP members and the international early childhood community, with a special focus on taking a child-oriented perspective. The OMEP research comprised four studies which are described in this paper. The rich data in the research were drawn from 28 participating countries, involved more than 44,330 children aged from birth to 8 years, as well as 13,225 teachers. These participants were from various early childhood educational contexts. The research methods used included child interviews, children's dialogues, and child-driven, theme-based projects as part of children's early education programs. The results showed that young children have significant knowledge about the Earth and important ideas about environmental issues, as well as knowledge of the responsibilities which individuals carry with respect to sustainability. In the research findings, it was strongly apparent that adults often underestimate the competencies of young children. It is argued that education for sustainability can be a driver for quality early childhood education.