This study investigated the influence of playing, upon the pediatrics microsystem during hospitalization time, considering the different points of view: the professionals, the pediatric patients' and the responsible for them. It is well-known that playing allows a hospitalized child move from the passive to the active position, what can be understood as a buffer in the development that faces social risks in a hospital environment. To better understand the multiple interactions, the human development we studied based on Urie Bronfenbrenner's ecological and bioecological theories. This research has a qualitative basis and to collect data observation and interviews were planned according to the Ecological Insertion methodology that has been adopted. It is a suitable methodological-theoretical way of getting reference for the research about the in-context-development in a real, natural environment. In order to get the most trustful answers, different kinds of strategies were necessaries: the first meeting: the researcher's ecological insertion; the preliminary study and the main study. It was evident that a hospitalized child needs much more than medicine, food, medical care, colorful environments and that playing is essential. Besides, the good interrelationships are important to potencialize development. Considering the idea that Environmental Education is an inter, trans and multidisciplinary task, leading to human relationship, the studies in this area point to new paradigms about environment, health and education. In this sense, , to change the hospital environment into a place of permanent playing, of learning and development, can improve patients' standard of living. In conclusion, the results suggest that a Physical Education and Environment Instructor insertion should be part of the pediatrics microsystem.