The prepuce is normally not retractible in babies. It becomes retractile in the vast majority of boys by puberty, and therefore should not require physiotherapy as done by you. Physiotherapy, as done by you, can lead to tears in the prepuce, and genuine phimosis which will need surgery. Therefore please leave your sons penis alone. However, if the urinary stream is thin, a surgeon/pediatric surgeon MUST look at the baby. From your description there is a chance that true phimosis has set in. Please consult a senior pediatric surgeon, or a surgeon if no paediatric surgeon is available.