//Any parents failing to keep their offspring under control should be asked to leave, whether they have had a drink or two or not.//
Quite correct, mamy.
it's not much use to other customers who are faced with unruly children spoiling their enjoyment if the keepers of those children linger for two hours over their two drinks. Even more problematic are the "Mummies" groups who meet in pubs and coffee shops. They usually have an average of two children each with them and simply sit chatting to each other whilst their Little Darlings run amok. The Wetherspoons' rule (if indeed it is a rule and if it is enforced) will not address that.
People who go to pubs, restaurants and cafes need to understand that not everybody is content with being disturbed by young children "expressing themselves". There are plenty of places where they can take their children to do that. They need to keep their children under control wher people are eating and drinking.