We have that same issue. Our daughter was in foster care, but I honestly don't believe that she has ever known what it is to be "full".
She eats CONSTANTLY, but we figure that with the adjustment, we will indulge her. As long as we are feeding her healthy foods (and the occasional not so healthy treat
), I don't worry about her overeating.
It is comforting to know, though, that we are not the only families that are dealing with this issue!