Animals don't make moral decisions, they're not capable of it, so punishing the Fox that attacked the twins in particular for doing it would be folly. Furthermore, how do you suppose they identify that individual Fox if it has already been escaped? They can't exactly have a line up of the suspects and make 'em do the perp walk.
This is all about keeping humans safe, humans are far more important than animals (which I think any sane individual can agree), and the process of transplanting the animals would be costly and adversely affect the ecosystem in which they're put. What so many fail to take into account is that if we put a large concentration of foxes out in the country, what do you think that's gonna do the fluffy bunny population in that area? Animals kill animals, it's what they're wired to do, and yet somehow when we do it--and we are animals--we're acting out of the natural order?
Now, I'm not saying we shoot them, then hang their carcasses from the lampposts as a sign to any future predators not to screw with us, but they need to be put down as effectively as possible for the safety of the human beings in the area.
p.s. Animals can't own land; that's silly. Furthermore, there was a time when Foxes did not exist, so this notion that they were always there is kind of silly. Before them there was another species, and before that another, going all the way back to bacteria. If you want to get technical, we stole this entire planet and the very materials we're made up of from single-celled orgasms, so I guess the next time you get sick, you shouldn't take anti-biotics or anything to fight the disease; after all the illness is just reclaiming what it's due...?