My son is 3.5 yrs old. on labor day he asked if he could go skiing on his own. We have been skiing together most of the summer and now he was ready to go alone. Used a set of unknown brand trainers with ropes tied between the front and back of the skis and the tower boom. he held on to the boom. I held on to the boom with one arm and held a ski with the other. This allowed me to keep everything in the right position.
Success. First time we cruised at 8 mph until i could not hang on any more.
The bindings were too big for him so next attempt, at the recommendation of a former professional show skier, we are going to have him wear water shoes inside the bindings.