There are loads of great places to mountain bike around the Croft from family friendly easy rides to hardcore down hill. Pitfichie mountain bike trails are about 15 minutes from the Croft, there is a cracking cross country trail which we use most weeks in the summer and a pretty hardcore downhill course. Ballater has lots of family friendly cycle trails and is about 30 mins drive away. There are a couple of good cycle shops in Ballater that we buy our bikes from, they also do bike rental and repairs. Electric bike rental is available at bike station, I have not tried it but looks like fun.
Glenlivet and Lagan cycle trails are fantastic; a bit of a drive away, but both are well worth a visit. Glenlivet is easily doable for a day trip.