Yep, I agree with what's been said. I think a lot of the trouble with the little breeds is lack of training...and their owners forgetting that they are still (distantly!) related to wolves. I have found (and not wishing to sound like I hate small dogs cos I don't) that owners of small dogs tend to treat them like toys & little people, & forget that they need to be treated like dogs. Small breeds are often pampered into believing that they are very high in the pack & therefore under pressure, they might snap or if accidently trodden on by a child, might react by snapping rather than backing off because they believe that they are higher in rank than a child.
Any dog can be a liability if they are not trained correctly, so a well trained Yorkshire terrier could be excellant with children & strangers or absolutely hopeless depending on its owners & how they handle it.