The research entitled “A Development of Mixed-age Curriculum to Enhance Early Childhood Development in Child Development Centers” aimed to 1) develop mixed-age curriculum to enhance early childhood development in child development centers, 2) study development of early childhood development in child development centers by using mixed-age curriculum. The target group of this research consisted of 2 groups of boy and girl early childhood with aged between one year and a half to three years in 1 small, 1 medium and 1 large sized child development centers under the Sub-district Administration Organizations in Muang district, Lam Pang province, teachers, administrators and guardians of the targeted child development centers. The research instruments were a handbook, and the mixed-age curriculum, a questionnaire for administrators and guardians, a questionnaire for teachers, test of early childhood development, and observation form for early childhood development in 2 aspects divided by the early childhood development. The data were analyzed by using the Index of Item Objective Congruence, mean, and standard deviation. The results of the study were found that ; The result of the acceptance of the teachers who used the mixed-age curriculum appeared that all 7 teachers or 100% accepted this curriculum. The analysis of the administrators responses appeared that the mean was 4.20 which was higher than the criteria set and it was in the most highly appropriate level. The analysis of the guardians’ responses appeared that the mean was 3.86 which was higher than the criteria set and it was in the highly appropriate level. The results of the efficiency of all three groups was higher than the criteria which represented that the efficiency of mixed-age curriculum was at the good level. The result of the analysis of the early childhood development in 2 aspects of 3 age ranges appeared that from the observation of teachers and the researchers found that the early childhood development in the emotion and mind and the society increased after using the mixed-age curriculum. When considered, it was found that early childhood with aged between one year and a half to two years had higher development than other age ranges. After the test of the physical and intellectual development of the early childhood in 3 age ranges, it appeared that the early childhood had higher development than before the experiment.