I have the same trouble with my 5yr old grandson. The doctors have put it down to "global delay development", which I take as they don't want to give a diagnosis or are waiting for more symptons. He is very quiet and shy but will stand up for himeself if bullied. He understands what I am saying and was toilet trained from the age of 2yrs. They are teaching him sign language at school but he can repeat words they are just not that clear and cannot put more than 2 words together, he also tends to use a soft voice. Allthough sometinmes he is loud and screams. It is difficult to watch them get further behind, they find it hard to have friends because they can't verbalise. It also creates self harming because they are not being understood. I just say do waht you can for them because you can't rely on the medical profession these days