What are the best places to visit in Scotland when traveling with two teenage boys and a 9 year old?

CHRIS H asked: We want to tour Scotland again, but this time want to be sure that the boys are somewhat entertained along the way.....hopefully this will make our travel experience more bearable! We have already seen Stirling, Glasgow, Edinburgh, Loch Lomond, Ayr and Aberdeen. Any thoughts on what would be interesting for all of [...]