Background and Objectives: Horse riding simulators (HRS) provide rhythmic, repetitive, and multidirectional movements analogous to horseback riding, which may facilitate postural control, balance, and functional abilities in children with cerebral palsy (CP). This study aimed to investigate the effects of the HRS application on the muscle tone of the lower extremity, gross motor function, trunk postural control, balance, gait functions, and functional independence in children with CP. Materials and Methods: A quasi-experimental study included 30 children with cerebral palsy (17 hemiparetic, 13 diparetic; mean age, 9.3 ± 3.2 years). All participants received Neurodevelopmental Therapy (NDT) for eight weeks, followed by eight weeks of HRS plus NDT, in a sequential design. Outcomes included the Modified Ashworth Scale (MAS), Myoton®PRO, Gross Motor Function Measures (GMFM)-88, Pedalo® Sensamove Balance Test (Pedalo® SBT), Pediatric Balance Scale (PBS), Trunk Impairment Scale (TIS), gait analysis parameters, and Functional Independence Measure (WeeFIM). Assessments were made at baseline, the 8th, and the 16th week. Results: At week 16, after incorporating HRS, all MAS parameters demonstrated greater improvements compared to those achieved during the first eight weeks of NDT alone (ES: 0.728–0.931, p < 0.05). Myoton®PRO measurements showed a significant reduction in gastrocnemius stiffness (ES = 0.672, p < 0.05) in hemiparetic children and decreases in hip adductor (ES: 0.649, p < 0.05) and gastrocnemius-soleus (ES: 0.766–0.865, p < 0.05) stiffness from week 8 to 16 in diparetic children following HRS intervention. Total scores on the GMFM-88, WeeFIM, TIS, and PBS improved significantly, with large effect sizes observed both from baseline to week 16 and from week 8 to 16 (ES: 0.771–0.886, p < 0.05). Additionally, Pedalo® SBT scores increased following HRS intervention from baseline to week 16 (ES = 0.599–0.602, p < 0.05). Conclusions: HRS integrated with conventional NDT may improve muscle tone, motor function, balance, gait, and functional independence in children with cerebral palsy, representing a valuable adjunct to standard rehabilitation. These findings provide the first evidence that simulator-assisted interventions may benefit daily activities in children with cerebral palsy.