If you want to convince yourself (because of bias) that something simply must have happened for these dogs to snap then sure, maybe it could be cognitive decline.

If we're being honest and logical, given the disproportionately large number of attacks are from pitties of various ages, they're just an inherently dangerous and unpredictable dog breed and noone can ever guarantee their dog won't attack a human for any number of reasons. Dogs can becone jealous for example, maybe the parents started to give more attention to their kids after a second baby? Maybe something the kid did (eg grabbing too hard) triggered the dog? Maybe that deeply ingrained wolf instinct to hunt was activated for whatever reason, eg the baby acted and reacted like prey? Who knows.