My son just turn 4 and he can't talk. He says everything but only i can understand him not even his dad can understand him. He talks to you and he makes sentences but he can't say it clearly.

Has his mouth been checked by a pediatrician? Or an ENT (ear nose and throat) specialist?

If not rule out any physical problem first.

You really need to have him checked out by a doctor. There could be something physically wrong with him and/or he may require some speech therapy.

I would go to a pediatrician or a speech therapist. My cousin didn't start talking til' she was 5. she needed a lot of help from the speech therapist.

My son was the same way. Speech therapy helped a lot. He's now 12 and was diagnosed with ADHD a while back, which also lead to his delayed speech.

The sooner you start seeing specialists and get help, the better off he'll be. Start with your doctor and go from there.

Good luck.