He needs a multidisciplinary approach from Paediatric Orthopedic surgeon, neurophysician, physiotherapist and rehabilitation expert. We also need to know about the amount of spasticity to assess whether it is treatable with just physiotherapy or along with it medication and/or surgical needs are there to relieve the spasms.
Next Steps
Use push knee split for 4-6 hours with 1 hour gap
Physiotherapy for lower limbs as follows
Stretching for hamstring, gastrocnemius and soleus muscles
Strengthening of quadriceps, tibialis anterior and posterior
All exercise 20 times with 3 sets per day
Health Tips
In very severe spasm condition, exercise are not possible to perform, in that case better to meet neurophysician and paediatric orthopaedic surgeon in person first