Kids pick it up really fast ...but they have to be ready. There can be some false starts, so if they get cold, scared, or aren't having fun, be ready to bail quick. My two boys learned at Hurricane Ridge. My best strategy for getting them under control was to ski down backwards wedging in front of them while bending over and holding their ski tips together with my hands. It made all the blood rush to my head, but they picked it up pretty quick.
But then, my kid's a badass: