The problem is with owners who claim to 'know' their dog, as in 'He won't hurt you ...' which sadly is am statement you can never make.
More accurate would be to say 'I don't think he will hurt you, he hasn't bitten anyone before, but if the mood takes him, then he will, and I have no way of knowing when or if that will happen, or advance warning if or when it does ...'.
Of course, any dog only gets to kill one child - so there is never any precident in the dog's behaviour - at least you would hope so!
Dog owners are anthropomorphic, and love to see their pets as 'part of the family'.
As far as I am concerned, a dog who has not bit anyone is not a dog who would 'never' bite anyone, it is a dog that has not bitten anyone YET - and that is an important and lifesaving distinction which needs to be observed rather more often than it is.
A dog is 'part of the family' insofar as it is a pack animal, and if it feels its place in the pack hierarchy challenged, by a new arrival being a typical instance, then it may well decide to 'deal' with the interloper, because that is what pack animals do.
Got a child? Don't get a dog. Having a child? Rehome the dog.