What age do children have to be out of a pub serving food in the UK?

Please only answer this question if you do know the legal answer. Our local (a popular chain pub/restaurant) pub is turning into a kids playground on an evening. We are used to it being treated like a MacDonalds but last night was the final straw when we sat next to a family of about 10 with kids ranging from 2 to 16. The kids were even being served at the bar at 9.15 pm (should they be at the bar at all?) They ran riot all evening until 9.45 and the adults were stinking drunk. We asked what time the kids would have to leave the pub and the manager said 9.30. At about 9.40 the manager announced that children should leave the pub by 9.30 and made a sacractic comment that "he apologised for having to make the announcement" but then the family ordered more drinks and were served. The manager made no further effort to ask them to leave. They littered the table and left such a disgraceful mess! The pub was full and it seemed that they were only interested in the revenue. Now I love to see well behaved families enjoying a night out and a meal around a table but this is ridiculous. We did ask the manager when we could expect some peace and quiet but he didn't seem bothered. There was a pub quiz which we couldn't hear because of the racket. I am going to make an official complaint to the pub chain but I do want to know what legal time kids should leave pubs. My family are voting with our feet and won't be going there again but it's such a shame that unruly, drunk families are allowed to take over our local pub in this way. Your advice would be appreciated. Thanks!