Culzean is a good day out, round the house there are the lego men to find, so wizz round there then find then explore the grounds, swan pond and playground. Watch out the toy shop and sweet shop can cause serious harm to your purse.
Burns cottage in Ayr. Just taken over by the National Trust, not been yet. Been in the visitor centre, nice cafe, opens out at the back to an enclosed garden with a play area, great to let them run about in as it is enclosed and only accesible through the cafe. I used to go whenthe kids were younger just to read a book while the kids played.
National Museum of Rural Life the farm bit is great, you go in the tractor trailer up to the farm. Can see the cows being milked.
David Livingstone Centre kids activities and trail through museum. Lots of references to lions.
Pollock house Ok it is another old house but the day we were there they had a murder mystery thing on with clues to figure out, the kids quite enjoyed that bit, although mine are older.
Further afield on Arran is Brodick Castle, seems to be a similar set up as Culzean, but not been.