He has taken Miles' toys/rattles/etc and assumed they were his.  The cutest thing is that he has taken Miles his toy, which we call his baby and dropped by Miles when he's crying.  Its adorable. 
Overall, he has been a wonderful big brother and we tell him that every day.  We still miss Charlie immensely and talk about him a lot, we wonder what he'd be doing right now and how he would interact with Miles.  We're pretty sure he's watching over his lil baby brother.