Common differences include:

He doesn't speak - but you know/think he can as you've heard him sometimes when he's on his own.  Possible reason - he may lack proprioception or suffer selective mutism (see exposure anxiety) 

He echoes everything he hears.  Possible reason - he may have a degree of neuro-developmental delay (NDD) + auditory differences 

He talks about the same things - over and over and over again.  This is often linked to anxiety 

He speaks too loudly or too softly or lack any expression in his tone. Possible reason - he has auditory differences which affect the way in which he hears. 

He find it hard to understand things.  Possible reasons  -  sensory differences;  sensory overload 

He use words that seem more grown-up than he is. This can be linked to serious illness at an early age but may also be associated with NDD. 

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How you can help.

It is always helpful to correct the underlying problems first but there are several approaches that may help from augmented communication to speech therapy - page coming soon.

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 A Personal View.

I believe that many of  the differences above are linked.  

Thus some illnesses, infections and fevers can contribute to NDD.  

Neuro-developmental delay often causes sensory differences - which can be exacerbated by gut and digestive issues.

Sensory differences shape the way in which the child perceives the world.

They cause numerous difficulties:

These include an inability to understand things that most other people take for-granted; an inability to read emotions;  sensory overload; cognitive differences and much more . .(see individual differences for more information)

They also make the world seem very frightening and can lead to great anxiety 

That in turn leads to obsessions and compulsions; a need for routine and a dislike of change

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