Not sure why pubs are for adults to be honest. Because people get there to drink and get drunk?
I am Spanish. I have lived in France, Switzerland, India, Ireland and, finally, in the UK. The attitude towards kids and pubs was something that took quite a long time to become familiar with. Kids stopped at doors like unwanted pets.
It is culturally acceptable to segregate kids in a pub. Would be unthinkable in Spain to stop a child entering a bar with his parents. I guess there are advantages to both approaches. But it is far from an objective truth that a place that serves drinks are food is, by nature, for adults.