have you looked at pontine or haven? we went to a caravan in downy last year on a caravan site called Bryn Morfa, it was ten minute walk (with kids, 5 with adults) to a very secluded and sandy beach, was lovely. you could walk in to town too so you had the castle. if you have a car you can take a trip to greenwood forest park which is a nature theme park for the under 10s which the kids loved. plus your an hours drive from snowdonia, 20 mins from the zoo, 10 mins from llandudno which has the great orme, the pier and the kids loved the speedboat rides.