hello mr upadhyay.a normal hearing is required for development of speech.your son may be having hearing impairment[difficulty in hearing],which is causing a delay in acquiring speech.please take him to an ENT doctor,his hearing will be tested by various tests like tympanometry
, otoacoustic emissions and BERA[brainstem
evoked response audiometry].a CT scan
of his ears may also be required.treatment will depend on the cause of his hearing loss
.once his hearing improves his speech will also improve.i hope he does well. dr praveen.