The main purpose of this research was to identify 4 to 6-year-old children’s ideas about microorganisms, taking into consideration the learning processes carried out in different educational contexts. To this end, data were collected from two institutions – a science museum and a kindergarten – by means of interviews, recorded conversations, drawings, and the application of a didactic sequence with the kindergarten group. A qualitative analysis of the data revealed that children associate the presence of microorganisms with dirty places and see them as pathological agents. The children demonstrated that they understand the idea of scale and the need for magnifying instruments. We found that they consider microorganisms morphologically simil...