Kids have been the least of my worries. Two of my three sons (ages 12 and 14, started flying at 7 and 9), do a credible job of holding heading and altitude, doing good coordinated turns, etc.
I've also flown a ton of Young Eagles around with nary a hitch except for the odd kid that tries to clown away his nervousness in front of his mates.
The adults are another story! I wasn't sure if I should post this in the "when you nearly became another statistic thread", but it really is a passenger from hell story.
The location was CZBM, (Bromont, Quebec, Canada) where I kept my PA28-140 (and now keep my Beech C23). Nice 5000 ft of blacktop, LOC/DME approaches, etc, with a built-in permanent crosswind or so it seems at times.
This day was sunny, hot, and particularly gusty. Took up a brother-in-law's mate. Did a nice preflight briefing except I forgot one essential detail: those pedals on the floor are not footrests!
So we take off, gusting crosswind from the right. Plane starts to veer to the left of the centerline (bad: glider strip in use parallel to the blacktop), so I crank 'er in to the wind, when the bird promptly tries to settle out of ground effect back on to mother Earth. No problemo, probably just a downdraft. Build speed back up, crank her into the wind again, and once more: mush back to earth. Hmm. Well let me tell you, even at 70 mph 5000 ft goes by in a hurry.
Now we're at the sweating, "what the f**k is going on?" stage. No more runway to play with, sick PA28 refusing to climb and a scared stiff passenger on his first light plane ride. Scared so stiff in fact....wait a minute, why is his left leg straight out and rigid??? Yep. He was depressing full left rudder. I hadn't noticed the rudder skew because typically I'd be applying right pressure at full power anyway with my left leg dangling; I don't feel movement so much as pressure and I had normal pressure application. Sho' 'nuff, the ball was askew.
The idiot had me doing a full rudder sideslip to try and stay on runway centerline. Now a PA28 on a hot summer day is no great performer. One in a sideslip is simply going in one direction: back down to Earth! So I yell out a "get your f*****g leg off the pedals" and whack him a good on on the thigh. Off came the leg, and now the good ol' PA28 rediscovered what it was built for and lept into the air and into a normal climb. B*****d didn't even offer to pay a share of the fuel for his ride.
You can be sure that now my briefing includes a "keep your hands and FEET away from the controls at all times". On occasion I might invite someone trustworthy to try the controls in SMOOTH weather.
I won't go into the barfing passengers stories (never happened to me but a buddy that flies my plane had it happen to him). Learned long ago, with novice passengers: smooth air, rate 0.00001 turns, etc.
Funny too: your best mates that you'd take up flying even if they took a vow of poverty, always offer to pay for some of the fuel. The passengers from hell, go free (and only once!).