The study aimed at assessing Problems of Curriculum Relevance in Enhancing Children's Cognitive Development in Early Childhood Education (ECE) in Ethiopia. An explanatory sequential research design was employed through a multistage random sampling technique to collect primary data from the participants (N[subscript i]=260) through questionnaires and observations. Descriptive and inferential statistics were used to analyze the collected data through questionnaires; thematic analysis was used for open-ended questionnaires and observation checklists. The first finding was that about 87% of the preprimary school teachers were not trained in ECE Curriculum. Secondly, the curricula under usage were poorly helped children daily to develop measuring units of the physical properties (length, weight, temperature, money, collecting & organizing information, and solving quantitative problems). Thirdly, teaching methodologies (discussion, categorization, explanation, and brainstorming) used by teachers contributed 79.21% to ECE Curriculum. Finally, lack of appropriate training, irrelevant curriculum resources, and teaching methods were the major identified problems in the ECE curriculum. In conclusion, the reasons for poor cognitive development identified in this study in Ethiopia's ECE Curriculum were poor teacher training and poor professional development, inconsistent and fragmented curriculum implementation, limited resources and learning material, inadequate implementation of play-based learning, cultural and language barriers, socioeconomic factors, and family support.