It is the fault of the owners.
Dogs are unpredictable pack animals, from the smallest to the largest, all have the capacity to turn and bite, or attack.
Any owner who says "He won't hurt you ..." is expressing wishful thinking rather than fact - more accurate would be to say "He hasn't hurt anyone yet, but he may do at any time ..."
Anyone who leaves a potentially lethal dog, much less two, in any circumstance where a child could be exppsed to it is being criminally negligent.
As I say, dogs are pack animals, and the arrival of a new baby pushes the dog down the pecking order. Most dogs assimilate their shift downwards in the hierarchy, but not all - as appears to be the case here. If one dog attacks, any other(s) in the pack will join in instinctively, with the tragic consequences that have made the headlines.
When ever dog owners say "Well, he's never done that before ..." with incredulity in their voices, you have to wonder if they are aware that the have an unpredictable and potentially savage animal as a pet, and they should train them, and keep them away from children based on that fact.
Dogs act on instinct, humans should know better than to initiate a scenario where anyone, much less a baby, can be attacked.
Lessons should be learned, but rarely are. All over the country you can hear owners of large dogs telling all who will listen "Our Mopsy is as soft as a brush, he wouldn't hurt a flea ....."
Oh yes he would ...