This is a post I made in another thread, but the concept works when introducing any new outdoor activity to a youngster, or anyone for that matter-- start slow, pick good weather, keep it fun. We have used this approach with our kids for skiing, backpacking , rock climbing, alpine climbing, winter camping and bike touring.
When we introduced our kids (4 & 6 years old) to winter camping, we started out for one night on a nice early spring day, and set up camp about the distance of a 10 minute ski from the snopark parking lot. The good weather made it possible to have an enjoyable time, and look forward to future trips. Being close to the parking lot made it easy to bail if things went sour. My wife was the backpacking and winter camping adviser for the area Boy Scouts. If possible, she would set up a similar scenario for the scouts for their weekend winter camping trips. I think she and our daughter may have gone on more Boy Scout winter camp trips than some of the scouts. Having a few good experiences under your belt really helps when encountering the "not so good" experiences.