How do you introduce a dog into your household with a child thats petrified of them?

I have a 3 year old and a 5 year old and its my 3 year old that is absolutely scared to death of any and all dogs but my husband and I have always had dogs and are now ready to have one again since we feel the kids are big enough but we know we are going to have to approach this situation with care cause if we get it wrong we know that Layla will be scared of dogs forever....Any suggestions?