Literature review shows that many primary school teachers have poor understanding of basic astronomy contents. Therefore, the aim of the study was to introduce specific astronomical content to in-service primary school teachers through two didactic games, to evaluate the didactic games and the teachers' knowledge and understanding before and after the implementation of the didactic games. The research included 24 in-service primary school teachers. The data were collected through the knowledge test (pre-post design) and questionnaires for each didactic game. The results showed that the teachers evaluated the didactic games as suitable for use in the classroom as they emphasized that they are educational, explicit and interesting. The implementation was identified as effective because the median for fractional gains was 0.54 and showed the medium gain in teachers' knowledge and understanding of selected astronomy contents. It was recognized that in-service primary school teachers do not feel competent for introducing complex astronomical contents to their students. However, the presented approach could encourage in-service primary school teachers to deepen their knowledge and to teach astronomy contents with a method that is closer to their students. University teachers could point out the advantages and disadvantages of didactic games in astronomy content and discuss them with pre-service primary school teachers.