DS always say things in third person. Ie. where do you want to go DS - he replies "DS room" or instead of saying I will get it (whatever it is lol) he says DS will get.. He never uses I, me, mine etc
that's also an age thing - kids need to be a bit older to make the transition from "name" to "I" (I can't remember exactly, somewhere between 2 and three I think, but could be wrong??)