This paper explores indicators of design fixation by following the development of the design ideas of a group of primary school children (age 10-12) carrying out a co-design project. Our goal is to find ways to improve the early mastering of DT (Diverging Thinking) and CT (Converging Thinking) skills, which in turn will help them to develop their creative abilities. The case study presented here indicates that the children showed adherence to the initial design idea and a lack of openness for divergent thinking at some points in the later stages of the design process, which led to little or no development of their design idea. Furthermore, we observed that the occurrence of design fixation in later stages of the design process has a negative influence on the creative development of the design idea. We grouped moments indicating design fixation into four categories that emerged from the data, which we named: “Band-aids”, “Already taken care of”, “Question not used for elaboration” and “It’s not possible”. We expect that these categories we found, which could be classified as indicators, will be helpful for a facilitator in identifying design fixation during the design process and adjusting the facilitation techniques accordingly. We expect these indicators to be present in sessions with students on different educational levels, which make these findings relevant to the education of future design professionals.