Hi, I've answered a bit but I'm not seeing it. I will start over.
The quick answer is that there is nothing to do to make his head grow.
Can you tell me why you want to do this? What is the problem you are facing?
Normally the way the head grows is that as the brain grows the fontanells separate a little bit (those soft spots that are not filled with bone) and make room for the brain to grow.
Having a small head does not affect intelligence or ability unless it is because the fontanells have closed too early. That is a problem caused synostosis, and it is discovered when a baby is showing signs of trouble with their brain and they go for an exam. The surgery done to correct this is a very big one.
I have ended the chat session and changed this to a question/answer because otherwise the site will not let us continue to chat without you paying more. As we haven't really been in touch yet I don't think that you should be paying extra. This way we can keep on corresponding without any extra charge.
Also, right now I need to leave the computer for a while, but I'll check later today to make sure you didn't have any further questions.
could it be caused by lack of sufficient nutrients at birth?i.e his having a small head as i see kids his age having much bigger ones?