It is well known that low back pain (LBP) prevalence is high during the course of school age children’s lives. However, literature concerning the initial onset of back pain between ages of 3 and 11 years remains scarce. The present study aimed to analyze the prevalence of LBP in kindergarten and primary school students. 278 (9.9±2.1 years old; 52.2% girls) students from two public kindergarten and primary schools in Valencia, Spain participated in this cross-sectional study. The Nordic questionnaire on LBP was used to ask questions related to the duration of LBP symptoms over time. The lifetime prevalence of LBP was 47.5% (n = 132), a last year prevalence of 44.2% (n = 123), and a last week prevalence of 18.8% (n = 50) was reported. Boys and girls reached lifetime prevalence of 52.3% (n = 64) and 47.7% (n = 82) (χ2 = 1.978, p = .099), respectively. By age group, lifetime episodes of LBP also showed a higher prevalence with increasing age (χ2 = 32.637; p < .001). In summary, our findings suggest that LBP increases with age. In addition, our results further strengthen the evidence that LBP onset could start as young as 10-years-old.