The construct that came into our lives with the term 'philosophy for children' (P4C) in 1970s is a method of developing critical thinking in children through philosophical dialogue created by the American philosopher Matthew Lipman. This approach is improved in cooperation with the enrichment of a group's point of view. The approach of philosophy for children is also known as 'philosophy with children' (PwC) promoted by different philosophers who have worked in this field in addition to Lipman's studies. The purpose of this study is to understand the effectiveness of philosophy with children curriculum on critical thinking. With this purpose, the following questions were asked: "What are the effects of the 'philosophy with children' curriculum on development of children's critical thinking skills?", "Does the effectiveness of the 'philosophy with children' curriculum vary based on the type of school they attend?", "What are the opinions of the children who participated in the ` philosophy with children' curriculum regarding this program?" The study used a quasiexperimental design without a control group. The pre-test and post-test data of the groups were collected using the "Scale of Critical Thinking through Philosophical Inquiry"developed for pre-school children. Additionally, in order to achieve social validity for the research, semi-structured interviews were conducted with the study group and the 3 teachers who acted as observers along the study. According to the findings, it was seen that the 'philosophy with children' curriculum was effective on critical thinking skills. According to the pre-test data, there was no significant difference between the critical thinking scores of the children at state school and the children at private school before the start of the program. After the implemented program, in the light of the post-test outcomes, the critical thinking scores of both groups were observed to increase. In both experimental groups, the overall scores and sub-scale scores of critical thinking were found "medium" in the pre-test, and "high"in the post-test. The analysis on the opinions of the students and the teachers on the program revealed that they generally had positive impressions.