In music, regularity is perceived as a highly ordered texture with prominent periodic patterns and strong neighboring relationships, in which musical ideas are organized in a way that the human mind can understand. In contrast, irregularity is experienced in an unstructured or poorly structured musical piece, where the relationship between patterns is rarely discernible and enjoyment is diminished by the enormous mental space required to process unique musical content. The interaction between regularity and irregularity in musical structure is one of the fundamental forms of musical expression used by composers across all musical styles (perhaps with different proportions in different aesthetics). Even though interest in children's folk songs has increased among ethnomusicologists, sociologists, educators, and folklorists since 1940, there is a lack of study on children's folk songs. The majority of research on children's folk songs is related to musical content, the social and cultural significance of children's folk songs and their relationships to adult music, the contribution of children's folk songs to cultural preservation, and the transmission of children's folk songs from generation to generation. Generally, the musical structure of children's folk songs is analyzed in terms of musical elements/dimensions, i.e., how the elements/dimensions are used (e.g., pitch span, use of meter, keys, rhythm, contour etc.). The impact of various musical elements/dimensions on children's folk song perceptions of (ir)regularity and complexity is mostly unclear. Although cross-cultural study on melodic complexity has been undertaken, the majority of it has focused on children's lullabies. There are currently no studies that use computational models to simulate the perception of (ir)regularity in children's folk songs. This may be because children's folk songs are generally considered to be regular, with a simple structure with repeated patterns, and even as a primitive layer of folk songs. The description of the dataset and link to the published research work are in the folder.