to OP.
Sounds like for your family situation, you may be looking for a real "mountain bike trail" but that's on the smoother, less technical, side of the "green" designation. If that's so, great news for you is that Charlotte area offers just that. Here are my top 2 suggestions for early entrants to MTBiking that hopefully not as intimidating. There're probably others, but I don't ride all the trails around C'lotte (actually LNSP has good options)
Southwest District Park (SWDP)
(You need to Login or Register to view media files and links) SWDP is a 2+ mile lollipop loop-2 way out and back then a loop) that can be ridden in either direction (because its not heavily trafficked) for variety, even though its signed to be ridden counterclockwise. Prolly toughest part for your family may be entering and exiting the trail on the slight hill immediately after leaving the parking lot. Its relatively smooth, as its not worn out from overuse and relatively level.
PS: A new extension is being added by some AWESOME trail gnomes to the Tamale loop within the trail that you may want to skip until it gets packed in.
Sherman Branch (SB)
(You need to Login or Register to view media files and links) Upon entering SB at trailhead, you are on a "service" road. Take your first right, and every time you come to it turn right. this will keep you on the smoother, less technical section of the Main trail. There's even a "short cut by-pass" that I suggest you initially take as your family's skills progress. However, near the end you may choose to walk the bridge section and the short rougher section immediately following it. Then eat lunch/dinner at Jakes Eat Place (they have hot dogs for kids, young and old ones).
A LOT of volunteer hours have gone into building and maintaining a FANTASTIC trail system approaching 200 miles of trail in the Charlotte+ area of all skill levels. You just have to spend a little time and effort to locate what works for you. As objective as we'd like a rating system to be, just use it as rough guideline. And, if necessary, like in your situation, do reconnoissance before to help insure a better outcome for your family.
To some of us, mountain biking is a great way to exercise, socialize, get away from the real world. I only wish I'd started my family mountain biking at a very young age. Hopefully, your family will give it a few more opportunities to pass muster.
This is a very informed and helpful forum of participants that have a wider variety of views that we'll willingly share, as you've discovered. However, your approach to getting information will probably greatly affect how/what/tone you receive it.