I don't know if the dialogue in AOTC could be altered to say he dreamt of killing the sand children and that he was angry at himself for even dreaming it (something to which Padme's response would be more believable).
But then when he has killed Mace in ROTS the line from the Dooku duel where Palpatine tells him he has done it before could be shifted in there and he could visualise actually killing them "What have I done".
Add that to Vader in his suit killing the younglings and you have a much more believable turn.