Due to the particularity of pediatric research, it is difficult to carry out randomized controlled clinical trials, so cohort studies are often used to evaluate the effect of intervention measures. Furthermore, with the rise of the concept of real-world clinical research, the number of cohort studies is also increasing. However, in specific disease cohort studies, there is a kind of bias that is often ignored by researchers, which leads to inaccurate research results, that is, eternal time bias.