The bond of the "blood" family is the predominant theme in this book. It is more powerful than "hunger": for food, for power, for lust...and like in many fairytales, love is wielded like a weapon to defeat evil. The children want to get back to their father so badly, that it motivates them to kill (granted it is in self-defense, but they still kill someone and that will change them forever). It is also interesting to mention that the step-mother in this story is portrayed in a negative light, further reinforcing the trope of "evil" stepmothers in fairytales. Perhaps this trope lives on to further push the idea that the bonds of blood can never be truly broken.
It is interesting to note that Gretel is the only female to survive this story. This seems to be the case because Gretel values love over everything else. Both the step-mother and witch are shown to be selfish and power-hungry. This characterization leads ultimate to their deaths. Still, the females in this story tend to hold the most "power". While Hansel is a resourceful child, it is Gretel that defeats the witch by pushing her into the oven. Just like it is the step-mother who convinces her spineless husband (the father) to abandon the children in their "best interest"; just like it is the witch who lures children with sweets. The women's prerogative definitely drives this tale.
Finally, I love the unique depiction of the witch in this story as a red-eyed, near-sighted, cannibal who has the same sense of smell as beasts. It just makes the villain that much more scary.