This study aimed to identify the different types of factual, conceptual and procedural errors among the six-years-old preschool children. The data were collected from 45 children from 3 kindergartens. The children responded to a Math worksheet which had 20 addition problems based on the early numeracy curriculum. The worksheet was validated by two experienced early childhood teachers. Both quantitative and qualitative methods were used to analyze the data. A total of 166 errors which occurred in the addition work of the participants were analyzed and categorized under 9 different types of addition errors. Further, the study revealed that 58% of the total errors were conceptual, 28% were factual and the remaining 14% were procedural errors in the addition operations. To gain deeper insights to the quantitative findings, seven children were identified and interviewed based on the nine errors. Findings from the interviews further corroborated the quantitative findings that, these children experienced misconception of mathematical knowledge, lack of procedural skills and memorizing facts which are inter related and precursors of each other. The findings of this study will facilitate teachers to adopt effective interventions and teaching methods to improve mathematical learning. The error analysis allows educators and content developers to understand the key development of young learners' knowledge and abilities in addition operations.