Thought I'd throw my .02 into this older thread. You know, this is kind of like the old discussion of when's the "right" age for a kid to walk? By golly, most of them eventually get it right!
Some are going to be ready at 3, some at 4, some at 5. I do agree that it's never too soon to get a kid into the whole routine/groove of heading out to go skiing, even if parents are doing a switch-off. Also lots of fun play-time in the snow, and some gentle sliding while being held.
I have but one, and he's a grown man now, but we started him for real on bonafide equipment at age 3 (he'd just turned 3). However, he did not "find" his edges until the following season, after having turned 4. Wow, what a breakthrough season for the kid
Anyone who has the capability to get their child into a season-long program, go for it.
When mine was 6, we did a week at Steamboat. He rocked it. Discovered tree skiing and "air." (He took me through some trees that were a tad tight for my at-the-time requisite 190s!)
I should copy this to the "my proudest skiing moment" thread. Watching that kid take off was, decades in retrospect, just amazing....I wish I could go back in time for just one day of that...