Thanks for posting your query here.
There are lot of things to consider -- i.e. what his development been like so far? Walking/climbing/Scribbling etc and what age they were achieved? Has he got any other medical problems or not?
From the details given, I would advise to get him checked over by a Pediatrician
or Developmental Pediatrician to find out what the problem is and treatment options accordingly?
If it turns out to be isolated speech problem, he may need to see a Speech Therapist to improve his speech.
Dr Tejas Shah