Singing in primary education has an important role in the teaching of Music Culture. Students love this activity very much and, with activity of listening to music, it is most often carried out during the first four grades of primary school. In order for singing to serve a purpose in the classroom, it is necessary to develop children's musical abilities. One of these abilities is voice range. Although everyone’s voice has its natural characteristics and limits in hight and depth, those limits can be expanded through systematic practice. This paper studies possibilities of children's voice, respectively their voice range. Also, the results were compared with the factors which are considered to have affect on that range to determine which factors really influence the development of children’s voice range. The research was conducted at elementary school located in Krapina-Zagorje County on a sample of 114 pupils. Data were collected through preliminary questionnaires for parents and teachers, after which a survey of students' voices was conducted. The results show that the child’s voice range has shifted toward lower tones that were thought children could not and should not sing. Factors that affect the extent of a child's voice range are their age, attendance at music extracurricular activities and music activities outside school (choirs, music school, etc.), to which we can add the frequency of the child's going to concerts with family members. Furthermore, differences were found between the class departments of students of the same age, and the frequency of teachers singing with students during the school day is also considered an important factor, not taking into account Music Culture lessons. Finally, it is necessary to adjust the default tonalities of children's songs in textbooks according to the actual possibilities of children's voices because significant differences have been identified, respectively most songs have an average higher tonal range than the actual possibilities of children's vocal range.