They were dealing with a guy that has already been charged with domestic abuse, fought off 2 or 3 police officers, 2 shots with a taser didn't slow him down one bit, and it appeared that he was reaching for something in the car.
Given those circumstances, it's reasonable that the police did fear for their safety, the safety of the three kids, and quite possibly the safety of the bystanders in the immediate area.
I do think all three cops should be fired for being pussies and not being able to subdue one guy without the use of a firearm.