On the basis of an increasing awareness about the importance of ecological questions and the need for a sustainable development, it has been argued that Swedish preschool children shall develop knowledge also about natural science. One important aspect of this is to make ecological phenomena visible in children’s every day life. The aim of the present paper is to report on a study of verbal communication between teachers and children in preschool about ecological phenomena. Children are here seen as active in their own learning and that develops on the basis of their own experiences in communication with the surrounding world. 21 children (3-6 years) and three teachers participate in the study. Six of the 21 children do not have Swedish as their first language. A preschool unit was followed by video observation during two months when working on themes about life in a tree stump and decomposition of leaves. Focusing the verbal communication the data observations have been transcribed. Then the transcriptions were analysed from the know-what and the know-how aspect of learning. The result is presented on the basis of the communication of the what-perspective and is discussed in terms of what is noticed and how the children’s understandings are communicated. Finally we discuss the connections between children’s ability to understand and communicate their observations, as well as the role of the preschool teacher and education for a sustainable development.