All sorts of things are dangerous in this world and if you have something potentially dangerous, like a car, pool, dog or gun then you have the responsibility to use adequate safeguards to protect your neighbors, but if someone disregards or violates those safeguards it's not the property owners fault. A 12' high fence I think would meet nearly everyone's standards for what is adequate to contain a dog.
Now myself, I have serious doubts about the veracity of this story. Either something is being exaggerated or left out. First off, there are almost no 12' high fences in residential neighborhoods and they nearly always require a permit. Second, I think it would be next to impossible to find a jury who would convict someone who had the dogs contained in a 12' high enclosure. Third, even if they did convict it would almost certainly be for manslaughter rather than second degree murder.
I also have trouble seeing this as being an incident that would be confined to pit bulls. Anytime you enter the territory of multiple, large dogs with aggressive temperaments you are taking your life into your hands. I could easily see this same thing happening with chows or rottweilers.
And BTW, I do not own pit bulls. I never have and likely never will. They're just more liability than I wish to be responsible for, but the key word is responsibility. People who don't take responsibility for their animals, (or in this case their children), are the problem, not the animals.
Pit bulls killed the toddler.