This.Jack Russell's are statistically quite high on the list of baby maulings, a survey a few years back revealed that the dog most likely to bite .......... is a Lab.
Dogs of any breed should never be left on their own with a small child, if they aren't old enough to know how to behave around dogs that means not in the same room alone. And for some children who haven't been taught proper behaviour that includes children at least up to the age of 6.