One of our 6 year old relatives visited on Saturday, and wanted to run the trains. After powering up the layout, and doing a few dry runs, I set the ZW-L throttle for the main line at about 7 volts. This was the "tested" voltage that would allow him to run the train at "full throttle" without attaining a speed that that would cause the train to derail. In no time, he was operating the train in forward and reverse, blowing the whistle, operating the cab chatter, and, inquiring if we could uncouple the cars on the siding -- far more sophisticated than I expected! [He is a big fan of the Thomas The Tank telecasts, and several other kid friendly railroad shows.] Without any coaching, he properly operated the switch track, backed up the engine and consist, and, with a little coaching, learned how to quickly double-depress the engine's rear coupler to detach the consist. He then pulled the train forward, and I showed him how to return the switch to the through position to run the engine on the mainline. After a couple solo loops, he wanted to add the cars from behind the loco on the other mainline to the cars in the siding, which we then accomplished together. We ran the trains for a while and had a lot of fun. He actually proved to be more train savvy than many of the visitors to the layout!
As a final observation, it became clear that the smaller controller size developed for the LionChief plus engines was an obvious asset, given his smaller hands. So, Lionel gets a "Plus' for that design also.