ds is a very articulate boy and is more than capable of having grown up, sensible conversations
so WHY oh WHY does he do "baby talk" ???
the only way i can describe it is he talks like a child of about 2 or 3 would. and he does it nearly ALL the time. especially when random adults talk to him, for example, in shops.
it is infuriating and above all, embarassing. as if the adult talking to him doesn't know me, they look at me strangely as if there is something wrong with him, or me :(
yesterday he did it in sainsburys when the checkout lady asked him if he liked school, and she must have thought i was awful when i shouted at him and dragged him away. 
he has a younger sister (dd aged 4) and she doesn't do it! she is a brilliant talker and talks far better than he does when he is doing his fucking baby talk.
anyway does anyone elses dc do this and what can i do to make him stop??