The only one I can speak of personally is Buffalo Mt trails south of Boone Lake(Johnson City I believe). It has 60 miles of trail rated (by Me anyway) as rather wimpy. More of a family trails system. I would not hesitate to take my 15 and 10 year old grandkids on those trail. They are groomed and smooth.
Not to be confused with Buffalo Mt trail in WVa (part of the Hatfield-McCoy system), which is more fun, but also rather groomed and tamed down from what it used to be 10-15 years ago.