The greening of schoolyards in Europe has a double objective: to make the city more resilient to climate change and to improve the daily living environment of children by reconnecting them to nature. In this context and in the framework of the European project COOLSCHOOLS, we are studying how children develop relationships with plant and animal species, and more particularly with arthropods (insects and spiders) present in their transformed schoolyards. How are relationships to nature expressed in children's daily practices and games? What interactions are set up between the children and the animals? What imaginations about nature are developed in connection with urban policies of transformation of schoolyards? Thanks to nearly 200 questionnaires distributed to the pupils and a first work of fictional narratives co-constructed with teachers, the relations between children and nature are explored. In parallel, interviews and focus groups with school staff, children and their parents make it possible to recontextualize these relationships to nature in the context of the greening of schoolyards.