All: Here is my update and a few additional questions.....

The update: We rented an Adams trail-a-bike yesterday and went out for about 2 hours (15 miles). Ben LOVED it - I even had to tell him to back off and NOT pedal sometimes so I could take a break. The hard part - Ben weighs just under 80 pounds and it was HARD to keep the bike stable. I tried to tell him to "pedal easy" and "look at my back" but there were a few precarious moments. I weight about 140. I spent a year on my bike travelling so my skills are honed. I use clipless pedals and had no issues there.

My additional questions:
1. Anyone have any opinions about the stability of the Adams compared with other trail-a-bikes?
2. I see some brands have 24 inch wheels vs. the 20 inch wheels. Any comments on the impact there?
3. The one we rented did not have gears. Any comments on the ones that do?

Thanks!!! Pat