I started my son this year at age 4. He really enjoyed it and got about 10 days of skiing in during our short season. I did not do a seasonal rental (mistake) and just used mountain rentals. This led to good days when the boots fit well and days where his feet hurt.
I did buy a Wee-Ski. Best thing I ever purchased. The Wee-Ski came with short and long harnesses. The short ones were great for teaching him how much fun skiing can be because I could ski with him, with me holding him up. All he had to do was keep the skis on the ground. I did the work and he got to experience the fun of going fast down the mountain.
The next step was to get him skiing independently in a wedge. I tried the tip clip, found it useless (but maybe I was using it wrong). I just skied backwards down the bunny hill with him starting/stopping in a wedge as I called out red light/green light.
Then we started working with the long straps. These are great for teaching turns. You really are like *pardon the expression* driving a horse. A little more pull on the left, he turns left. On the right, he turns right. He got the feel of skiing on his own and making turns.
Magic carpets are cool, but find a mountain with a small lift on the bunny hill. Ours was Tuxedo Ridge in NY. That taught him to get on/off the lift. He had it down by the end of the year, and he was going on bigger slopes by our last time out 2 weeks ago, using the long harness.
Next year, I will either get a full season rental from our local ski shop or just buy (I have a 1 year old daughter who was eagerly eyeing my son and I as we can down the mountain). Of course, I wonder about buying considering my son is very big for his age (45 inches, 43 lbs) and my daughter is tiny for hers.
I am only sorry the season is over out here.