We'll be in lower GB for 7 days during Tgiving week. We'd love to take our kids to a Medieval Banquet in a castle (they're 9 and 10.) Ruthin doesn't have anything going the dates we're there. Our target travel spots are London, Stonehenge/Avebury, Cotswolds, Ironbridge Gorge, maybe Windsor/Cambridge. If anyone knows of a good castle banquet near any of those spots please let me know. I'd also welcome any "don't miss" spots that 9/10 year olds might like. Thanks!
Can't speak to the banquet, but be sure to take them to see Windsor Castle. Our kids love the displays (son especially loved the armor and weapons) when they were the age of yours. The Tower of London is also great for kids.
There is a place at St Catherine's locks near Tower Bridge and Tower of London. It is not a castle, but looks interesting.