I had a day out in South Ayrshire and visited Culzean Castle and Dunure Castle. They are only a few miles apart and can be easily visited on the same day. Dunure Castle is largely derelict and is free to visit. Culzean Castle and Country Park is cared for by the National Trust for Scotland. It has lots to keep a family occupied for the day https://www.nts.org.uk/visit/places/culzean