This article describes the didactic principles underlying the creation of a ready-made fifteen lesson plan package for primary CLIL (for Maths, Geography and Science) for pupils aged 5 to 12, developed through the collaboration of an international group of English and primary teachers, teacher educators, researchers and teaching materials developers across four European countries in the framework of the CLIL for Children (C4C) project (2015-2018) on educating teachers for CLIL teaching environments. These principles are presented in the framework of a brief state-of-the art discussion on the lack of ready-made teaching materials for CLIL, their importance for teacher development and quality teaching and learning in CLIL classrooms, and criteria they should conform to. The article proceeds by summarising the findings of two C4C surveys, one on best CLIL teaching practice through national reports of four European countries (Italy, Portugal, Poland and Romania) and the other on Open Educational Resources (OER) available for CLIL Maths, Science and Geography, as well as by drawing on C4C Guidelines. The article then demonstrates these principles in practice through a module of a three lesson plan sequence for CLIL Science on the topic “The World of Plants” by showing how language (vocabulary or content-specific terminology and language functions), specific communication skills, content and culture are integrated and developed through a child-centred, holistic (Brooks and Brooks), constructivist approach. Digital technologies are included as everyday learning processes for access to knowledge and playfulness in learning. Methodologies for active, experiential, discovery, problem solving and cooperative learning are foregrounded. The article further highlights how teacher cooperation and teacher identities (English and primary education teachers) as individuals with multilingual repertoires, expectations, and expertise are crucial for producing quality CLIL materials and resources.