Good on them - I have 3 Young children and wouldn't dream of taking them to a pub to eat
Why not? I take my young DC to the local (gastro)pub fairly regularly and they're almost always really well behaved. If they weren't, DH or I would simply take them out immediately to avoid disturbing other diners.
Having said that, I actually do agree with this pub's decision, as there are a lot of families who don't help their kids to behave correctly when in a pub/restaurant setting - instead they just ignore them, the kids understandably get bored and run riot, disturbing other diners. It's not the children's fault obviously - it's the parents.