Simple, there are some that are "family freindly" pubs with meals and outside playing areas which are fine as well as catering for Sunday Dinner otherwise pubs aint for kids.
Quite difficult in London as land is an issue, but your traditional country village pub with childrens amenities (mainly in our very short summer) is part of British culture. We use to have a ball in summer with our pop and crisps in the beer garden.
I do not care for children in pubs ouside the above criteria.
I think it's cool as long as children understand that when they are in a pub, they are being allowed to "join in with the adults" and behave accordingly. Pubs aren't playgrounds, and they're not at home.
I suppose the same rule applies to everyone in the pub: show consideration for other customers, and we'll all get along just fine.
I'm not too keen, but as usual it falls on the parents to show responsibility for them. Usually when children trigger my grumpiness in pubs it is when the parents are trying to pretend they don't exist. This can come in many forms. In a recent trip to the newly refurbed Queens Head I was told by the 8 year-old collecting glasses that she "hated her life" and that she had been there all afternoon. Her mother then told her to stop moaning as being in the pub was "brilliant!"
In the Salisbury I've seen parents letting their little angels howl at the moon while they bury their heads in the Sunday papers. Almost like being in the pub temporarily absolved them of any parental duties.
Parents, you've been told. Pay attention to your kids so I don't have to! :)
BTW, I can't recommend the Queens Head. No under 21's my a**e.