I think that it depends what sort of pub it is. A lot of 'pubs' these days are just chain restaurants with a sort of pubby look. I have no problems with children in these, in fact I take my (well behaved) nine year old grandson to one of our local ones which he regards as a great treat.
However I wouldn't for a second think of taking him into a real pub such as the Victoria in Lincoln, nor would I want to see other children in there. What is wrong with adults wanting their own space anyhow? There are stacks of pubs that are appropriate for children, please leave the few proper pubs for the sole occupation of grown ups.