My wife and I use the trail gator's for hauling our kid's bikes around. I've never had the problem you are talking about with them off balance. I have ours attached the seat post right below our seats. I just made sure they were fairly straight and secure, but I didn't take any kind of special effort to true them up or anything. There are a couple of caveats with using them:
1. You have to compensate for your child's lack of balance. You can feel them squirming off balance as you ride. Mine eventually chilled and it wasn't very noticeable most of the time.
2. It's much much more energy to haul trail gator + kid's bike + child. A really good workout. I think I calculated like an additional 100lbs with the whole rig. ;)
3. Your child needs to participate for the best experience. I took them around the cul-de-sac several times to get them used to it. They need to know how to lean on turns. Not to hit their brakes (You will totally feel this!). And how to pedal a little to assist.
I think they are pretty cool once you have them working.
