This paper reports on the thoughts 6-year-olds and 9-year-olds have related to the serious issue of air and sea pollution. More specifically, twenty seven 6-year-olds and thirty 9-year-olds attending two state schools in Volos, a small provincial town in Greece participated in the research which assessed the students' competence to think systemically about dealing with pollution. The study sheds light on whether students are able to identify interrelations between the components of pollution, and clarifies the mental models they hold. Data was collected through drawings and interviews, subsequent analysis of which indicates that students appeared to hold two mental models related to pollution; pollution is connected both spatially and temporally with visible pollutants; and, pollution is connected indirectly with invisible pollutants. The students seemed to exhibit a kind of systemic thinking, which was done unconsciously to a certain degree. Thus it is a challenge for education to enhance students' systemic thinking in an attempt to bring it to a more conscious level, which will assist them to reconstruct their mental models of pollution.