A dog will always have a tendency to lean toward its breed-specific traits. Terriers were bred to be fearless fighters. Pitbulls on top of this have extremely powerful jaws. In my experience, pitbulls are generally very affable towards humans, but if you take in a rescue, there is an element of uncertainty, especially in the first days and weeks as the dog is still learning who its new family is.

Historically deaths by dog attacks correlate to the size and power of the animal, along with which large, powerful breed is currently in vogue with a certain type of owner, not necessarily the aggressiveness of the breed. A Yorkshire Terrier may be just as prone to bite as a Shepherd, Pitbull, Malamute, Rottweiler or Doberman, but the damage they can inflict is limited compared to these latter breeds. Any of these powerful breeds can be lovely dogs if raised the right way. The problem comes when either they are mistreated or intentionally raised to be aggressive.

Specifically, this wording is:

The most aggressive dog I've ever owned was a female beagle -- oh, what a bitch -- and the older she got, the meaner she got (just like me!). That dog would bite you just as soon as look at you, little nips, you know? All the time.

I think the stats bear me out that little dogs bite far more frequently than bigger dogs. Obviously, bigger dogs do more damage when they bite, but those bites occur far less frequently than chiuauas.  

Now here's where I go out on a limb. Personally, I wouldn't leave a three year old alone with ANY dog, much less a pitbull. Dogs don't just "go crazy" and attack -- they're provoked. But a three year old can grab and poke and smack without realizing the effect that's having on a dog. I'm not saying that every dog attack is provoked. I'm saying there are warning signs a dog is going to attack. It comes back to supervision, which is an owner's responsibility. 

Pits are strong dogs -- they're quick and they're tenacious. They can play rough. It's up to the owner to establish the boundaries of play and know his/her dog's temperament. I know my dog's triggers and I know my dog's moods. I am a responsible owner. But I'm not stupid, either. He's well trained and I don't put him in situations where he's out of my control. 

My wife once got out of our car and was attacked by a dog. I couldn't get out fast enough to do anything before the owner managed to pull it off her. I would have kicked that dog from pillar to post had I managed to be nearer. I know that sounds horrible, but my lasting memory is that I was not fast enough to get my wife to safety and from that moment on, the above has been my first thought with every dog that runs towards my family.

I just returned from visiting family and they have two cats. I had cats growing up, but not my little kids. So they needed to be shown how to treat them. My 9 year old was fine. My 6 year old was... ok... but I had to watch her, carefully. Spook a cat, don't respect their personal space, rub them the wrong way, and...!