Foot mobility and strengthening treatment (FMST) is a routinely practiced management strategy in musculoskeletal rehabilitation to improve ankle and foot alignment and muscle function, which prevents joint deformities. The FMST may contribute to improvements in foot alignment and muscle function in children with cerebral palsy (CP). However, treatment influence on muscle imbalances and strength in children with spastic diplegic CP is not yet documented. The aim of the study was to determine the effect of FMST on tibialis anterior (TA), medial gastrocnemius (MG), peroneus longus (PL), and soleus muscle activity using electromyography (EMG) in children with spastic diplegic CP. Twenty children with spastic diplegia (mean age: 7.4 years) with GMFCS levels I, II and III were included in this pre and post-experimental (preliminary) study. Muscle activation of TA, MG, PL, and soleus was recorded using surface EMG in a standing position before and after providing the intervention. Muscle activation in RMS-EMG (mV) was calculated. Findings showed a significant increase in muscle activation of TA, MG, and PL in standing position following the intervention. The increase in soleus muscle activation in standing was not statistically significant. We hypothesized that FMST could alter the muscle recruitment pattern. Our findings showed immediate improvement in muscle activation after the intervention. Future studies should consider its carryover effect on motor performance and gait using functional outcomes.