My ds is 7 nearly 8, (asd) to give a bit of background, he didn't speak at all until he was 3 and when he did he spoke only in repeated phrases usually from Thomas the tank engine!
His speech has improved over the time he's been at school although he rarely speaks to people he doesn't know well and only speaks at people (very poor conversation skills) instead of to them. Most of what he says is fact based or lists. And he uses very long words he sounds like a little professor when he speaks although sometimes the words don't necessarily fit.
He also stutters a lot this is getting worse as he gets older.
Over the last few weeks I've noticed that he started changing the f sounds in words when he speaks e.g foot becomes thoot, or Friday becomes thriday. He doesn't have a lisp it's a deliberate change of the sound, he definitely isn't aware he's making a mistake when he says these words but he used to say them properly. He's now started to do it with other sounds but f/th is definitely the most regular. It's making his speech less understandable.
Other than just keep correcting him when he does it is there anything I can do to help him, or does anyone know why he might be doing this? People have noticed and I'm worried that the other children will be nasty to him about it when he goes back to school!