A tavern can be used to mean any of the above; it has to be compared contextually with the rest of your information. For the most part (having lived in both England and America), I would have to state that a tavern is an establishment one would frequent for the purpose of sharing a laugh and a drink with friends, as well as a light meal. I would bring the kids to a pub; I would not bring the kids to a tavern. In order of "family friendliness," I would rate the four terms as follows:

Restaurant - primarily visited for a meal; usually easy to order a beer as well (although not always spirits)
Pub - primarily visited for a quick sit-down meal, with a guarantee that the proprietors serve beer and, most likely, spirits
Tavern - A watering hole that offers a cold sandwich or bowl of stew, at best, and only as an afterthought
Bar - Liquor and, oh by the way, peanuts

Hope this wasn't too confusing!