The use of energy is one of the most important anthropogenic environmental issues of our century, as from its production, disposal and use there are many negative effects on the biotic and abiotic elements of the ecosphere. Reducing the environmental impact of the use of matter and energy is a key educational issue. Students are the future adult citizens, who will make decisions for themselves and their fellow human beings. For these key reasons, Primary Education plays an important role in raising environmental awareness and shaping the behaviours of critical children, who need to be oriented towards a sustainable future through their energy literacy, in the context of sustainability education. The purpose of this study is to capture and highlight the basic knowledge, perceptions and daily practical functions of children in the use of direct-visible or otherwise functional energy, which is perceived in children relatively easily, directly and quickly and then their correlation of the findings on the effectiveness of children's taught energy literacy in their school education. The sample of the study consisted of 132 students of 5th grade of 3 Primary Schools in the city of Rhodes. The data collection was done using a structured and anonymous questionnaire and the questions were mainly closed type. Issues of anonymity and ethics were observed. Data were analyzed using the statistical program SPSS 25. The results of the study reveal lack of knowledge and misunderstandings in matters of forms and sources of energy, in the view of oil by several children wrongly as a Renewable Energy Source, in the knowledge of the unit of measurement of electricity, in the type of main energy sources in Greece and Solar energy as a form applied in Greece, a country with more than 300 days of sunshine per year. The concepts of energy efficiency and climate change also indicate the need for retraining, while carbon dioxide emissions are wrongly linked to the use of solar energy. Regarding the individual practices of energy austerity, saving and rational use of energy, they seem to be at a fairly satisfactory level compared to knowledge. In particular, children state that they reduce electricity as they turn off most electrical appliances after use, they turn off the lights in places they do not use while the use of energy-saving lamps seems to prevail. In cases where heating is needed due to cold weather, children state that they prefer to wear more clothes than to increase the heating degrees of the thermostat, while, when ventilating the premises, they turn off the heating (or cooling) sources, contributing significantly to the energy and environmental economy. Undoubtedly, there is still, albeit to a limited extent, the possibility of further improving them for a small number of students. The results briefly show significant misunderstandings in matters of knowledge and deficient energy behaviour regarding the use and reduction of energy by a small number of children. The need arises for the retraining of children in an active experiential way through well-designed Education and Sustainability Education programs, as the development of ecological awareness is an important educational goal for the formation of energetically literate students.