I know of very many country pubs where no one bats an eyelid at the presence of children, even after the 9pm watershed. They are usually with their parents/families, are not drinking alcohol and come to no harm (at least since the smoking ban was introduced). Families with children can be in restaurants, hotels, or indeed at home when adults are drinking alcohol, what makes the pub so different?
I think there is very probably a country/city divide on this issue. In the country the pub is often the social centre of a community, and many events take place there that would naturally include children. I remember Mairéad Ní Mhaonaigh (of the group Altan) on the radio at the time the 9pm ban was introduced. She explained how she practically grew up in the pub in Gaoth Dobhair, that the pub was the place where traditional music was played and passed on to youngsters, and that she thought the ban was a mistake.