Thanks all for the quick feedback. It certainly helped. We had a meetup, only the 2nd one, scheduled for yesterday evening to discuss the project. Quite a bit of course correction was achieved.
As Oldscout448 brought up, I took a closer look at the BSA safety guidelines. For the scout's age, he is able to use a 'screwdriver (electric)', so that opened up doing assembly for him.
In the meeting, I told the scout, I'll wrap up the assembly model (was nearly complete already) and I'll pass on a pdf of the assembly model and an exploded view of the cart. The rest of the piece drawings