It depends on the dog, really. But I have to second that pugs are great with children. They tend to be happy and playful and small enough not to be as much of a hazard as a jumping Lab or Golden, if you go for a puppy. Boston terriers, too, are a great all around dog.
Vicious? Any poorly bred or dominant personality dog that is bred for aggression and then poorly trained or socialized. (Strong emphasis on the poorly trained and socialized!) If you are not dog experienced, and unsure if you can handle a strong temperment, go with a "soft" breed. Dogs with dominant temperments are not for everyone.