Hi Married, There is nothing in this world that cant be cured beside Cancer,AIDS etc. I am a Psychologist from California. I do believe in home Therapy . I had 2 cousins  who were the same. They were beaten up by their dad when they were young. The dad (My Uncle) who is an Engineer  wanted his children to be an engineer as well. Uncle hit them bad for them to study hard and get good grades. Thats how they started " Bhak Bhak"  . They lived with me for 2 years ( My cousins). I really wanted to help them. I actually helped them at home. The doctors cost too much for the sessions.
Here is a Mantra which will do good. You just have to believe in it. Chant any time. The more you chant the better for you!! Please keep me update!!

The Maha Mrityunjaya Mantra - The Life-Giving Prayer

Om trayambakam yajaamahe sugandhim pushtivardhanam

Urvaarukamiva bandhanaan mrityor muksheeya maamritaat.

Make  him speak slowly.
Make him repeat the words.
Go on the internet and type " Speech Therapy" on Google , and make them hear it as well as repeat it.
Make this a routine every day for Speech.
You can help him so much if you really want to.
Dance Zone