I've never stayed at Craigendarroch itself, but we have stayed with my husband's family who live very nearby. When we last stayed my children were 6 and 9 and there were younger cousins involved, so that was a major factor in our activities.
We visited:
Braemar Castle - built by the 2nd Earl of Mar in 1628 and a key site in the Jacobite uprisings. On the day we visited they were staging a re-enactment of the call to arms for the second uprising, and had various activities on the grounds throughout the day.
Scolty Tower - A relatively easy walk with young kids and nice panoramic views of the surrounding countryside (but otherwise not much to see here).
Muir of Dinnet National Nature Reserve - A short walk from the visitor centre here takes you to the Burn O'Vat, a large cauldron-shaped cavern that can be entered through a crack in the rocks. My kids loved this place, particularly climbing up the boulders on the far side of the vat!
The furthest of these (Scolty) is within a 45 minute drive of Craigendarroch.