I must have raised my kids in the dark ages also because Medussa's post sounds like what I did with my kids. For some reason they just knew what their behavior should be in a public place and we never had a problem taking the kids with us. One thing I've noticed in restaurants is if the parents are loud the kids will also be loud. We always make a point of thanking and congratulating parents with well behaved children in a restaurant or other public place.
You seem to be on the right track with your 4 yr. old and I don't think you need a book to continue with the manners.