It's possibly a cultural thing. There's nothing wrong with taking children to a bar that serves food in Australia -- I've done it many times. Similarly in the UK. We didn't have children when we lived there, but family meals at a bar were quite common.
The bigger question is what are those parents doing taking their kids to The Strip in Las Vegas in the first place? I was there last month and I quickly decided that I'm NOT taking my kids there. The Strip is really designed for adult entertainment. Some of the shows and places are suitable for kids, but the streets aren't.
As a general rule, I agree with laws that ban smoking in food serving areas, and in places where large numbers of people congregate. As has been discussed ad nauseum above, my belief is that while adults should be allowed to smoke, I disagree that they should be allowed to subject others to the effects of second-hand smoke. Customers have the option of not being there, but employees don't -- or, rather, the option for employees is a lot more serious (ie. loss of a job) if they want to avoid exposure to second-hand smoke.