The only thing that bothers me is the time traveling thing. They could just use it to go back and kill voldemort when he was a kid. They say it's dangerous to use but Dumbledore let Hermione use it so she could attend several classes simultaneously for Christ's sake!
Personally I think that's one of the "common sense" things of time travel if you think about it actually. Time travel is dangerous; but only if used on a grander scale to effect scope-changing events. Such as how it might be dangerous to, for example, go back in time and assassinate Hitler because there's no telling what the world would be like today. It would change so many variables about history that you literally run the chance of ending the world because major events X and Y combed with smaller event Z to make things worse than they originally were due to the sheer unpredictability of that chain reaction.
Where as it's (by comparison) incredibly easy to account for things that might go wrong with little Susan Smiley goes back in time to both watch the TV movie she wanted to see and
finish her homework. Smaller instances of time travel like that are less likely to be "dangerous" by comparison. But that's just me theorizing aloud.
Of course keep in mind this isn't even getting into the other popular theory of time travel: That every decision you make generates an alternate universe for that decision's pathway. Meaning that even if someone went back and killed Voldemort as a child it would only result in a split timeline; doing nothing to change things in the original world.