Objective To explore the influencing factors of flexible flatfoot in preschool children and the therapeutic effects of orthopedic insoles intervention. Methods Convenient sampling method was used to select 1-to-6-year-old children who visited the Prosthetics and Orthotics, Department of Rehabilitation Medicine at the First Affiliated Hospital of Sun Yat-sen University between April 2019 and December 2023. According to the follow-up visits of children wearing orthopedic insoles after 1 year, the follow-up group was divided into the experimental group, and those who did not follow up were matched with the experimental group based on general information to form the control group. The degree of flatfoot of both feet, hallux valgus angle, heel valgus angle, knee valgus angle, navicular drop height, tibial torsion angle, foot posture index, and joint flexibility of children at the initial visit and follow-up were evaluated. Ordered multinomial logistic regression analysis was used to assess the factors influencing the degree of flatfoot of children’s feet. Results A total of 976 children were included at the initial visit, all wearing orthopedic insoles. Among them, there were 805 cases in the control group and 171 cases in the experimental group. There were no statistically significant differences in gender, age, height, or weight between the two groups (P>0.05). A comparison of the experimental group before and after wearing orthopedic insoles for 1 year showed that the degree of flatfoot of both feet, heel valgus angle, knee valgus angle, foot posture index, and joint flexibility were lower at the follow-up visit than those at the initial visit (P<0.05); the remaining parameters showed no statistically significant differences (P>0.05). At the follow-up visit of the experimental group, both heel valgus angle, knee valgus angle, and foot posture index were lower than those in the control group (P<0.05); the other parameters showed no statistically significant differences (P>0.05). Age and tibial torsion angle were negatively correlated with the degree of flatfoot (P<0.001), while hallux valgus angle, heel valgus angle, knee valgus angle, navicular drop height, foot posture index, and body mass index were positively correlated with the degree of flatfoot (P<0.05). There was a difference in the degree of flatfoot between male and female children (χ2=99.76, P<0.001). The results of the logistic regression analysis showed that navicular drop height, male gender, foot posture index, body mass index, heel valgus angle, and age were influencing factors of the degree of flatfoot (P<0.05). Conclusions The flexible flatfoot in preschool children is influenced by factors such as navicular drop height, gender, foot posture index, body mass index, heel valgus angle, and age, and it will be somewhat alleviated as they grow. Wearing orthopedic insoles can correct related biomechanical abnormalities of heel valgus and knee valgus to some extent, but it cannot significantly reduce the degree of flatfoot.