Background Adequate and efficient standing postural balance is key for functional walking and handling abilities in children with spastic diplegia. This study was designed to evaluate the effect of kinesiotape applied on ankle dorsiflexor muscles on balance in children with spastic diplegia. Thirty children with spastic diplegia of both genders participated in the study: 16 boys and 14 girls between 4 and 10 years old. They were divided randomly and equally into two groups: a control group, in which children received the standard physical therapy program for children with diplegia; and the study group, who received the same physical therapy program as in the control group but after kinesiotape application over the ankle dorsiflexor muscles. Both groups received the treatment program for 1 h, three times per week, for three successive months. Postural stability was assessed through evaluation of three stability index (anteroposterior, mediolateral, and overall) for all children by the Biodex Balance System before and after treatment. Results Statistical analysis of results before and after treatment was performed by mixed MANOVA to compare effects both within and between groups on stability indexes, and post hoc tests were carried out for subsequent multiple comparison. The level of significance for all statistical tests was set at p < 0.05. Before treatment, there was no significant difference in the stability index between both groups (p > 0.05). Comparison between both groups post-treatment revealed a significant decrease in the measured variables of the study group compared with that of the control group (p < 0.05). Conclusion Adding ankle kinesiotaping over dorsiflexor muscles in conjunction with a balance and gait training exercise program for children with diplegia can enhance postural stability and decrease sway. This study suggests that it should be added to the treatment program for children with diplegia. Trial registration This study was registered retroactively. Identifier: NCT04243928