Just wondering, as have been discussing this with my sister who's an infant school teacher. Her theory is that children do in general interpret language very literally, certainly during their infant school years, and do not always understand idiom, jokes etc. For example, she once used the phrase 'we're going to kill two birds with one stone this afternoon' in referring to a planned activity with her class of 6/7 year olds, and they were all horrified at the thought of throwing stones at birds and spent the afternoon telling her it was wrong to kill. Now that is the kind of reaction you might definitely expect from a HFA or 'aspie' child, but these were all NT children.
My DS is now 5 and there are times when I think yes, he's starting to recognise and interpret language in the way an NT child might. For example, I might say 'wow that's a great lego car DS, well done' and his response will be 'yes it's fantastic isn't it mummy, it's really cool' - so understands that 'cool' can mean 'good' as well as 'bit cold'. But at other times he very definitely demonstrates a literal interpretation of what I have said and gets unsettled - on the way to swimming in the pouring rain the other day I said 'goodness me DS it's raining so hard we won't need to get in the swimming pool, we could just jump into a puddle' as a joke, and he got upset and tearful and said 'but I really want to go into the swimming pool I don't want to swim in puddles'.
I am not sure if the above is an early indication of my DS struggling with literal language interpretation, or simply typical of his peer group. Certainly at the moment many of his friends are similar - my SIL was telling me recently that after her DS (4.5, NT) had eaten a huge tea, she'd joked with him that if he ate any more pudding 'he'd explode' and he started crying.
So, at what age does it become clearly obvious that an ASD or Aspergers child is continuing to interpret language and sayings etc very literally whilst their NT peers develop the ability to interpret 'correctly'? I put 'correctly' into inverted commas because let's face it a lot of sayings and language phrases that NT people use are actually, when you think about it, quite ridiculous, and in many ways the ASD 'literal' interpretation probably makes a lot more sense!