Advance preparation should include leaving enough time to get to your destination. Don't show up right before your child's first ski lesson begins. There will be paper work to fill out, and fitting for rental equipment can take time. Some ski resorts offer ski rentals the day before a learn to ski package begins, just to save time in the morning, when people are eager to hit the snow. If you rent from a ski shop close to home, you can spend more time focusing on fit, but you'll have to lug equipment from the parking lot.
Since most first-time skiers take group lessons, young children should have some prior group experience. The added stress of being in a group situation for the first time can make 3-year olds anxious. Private lessons are always an option, but since kids learn from kids, and group ski lessons emphasize fun, your child will likely have a better time -- and learn more -- in group ski lessons.
Being happy on the slopes often means being dressed appropriately. Dress your child in layers so she can peel off or add on a layer as the weather changes. Many first-time skiers think they need several pairs of socks, but this makes it hard to fit boots. One pair of light to medium weight socks is best. But bring a spare pair of socks for every member of the family, in case one gets wet.
Many ski resorts will not even let kids on the mountain without a helmet, and investing in an adjustable fit helmet can save money in the long run. If you buy a helmet in advance, you can also get a thin hat or headband that fits under, to keep your children's ears warm. Look for a helmet that is specifically designed for skiing; bike helmets will not do the job. Sunscreen is necessary, not just for sun protection, but also against the wind. Special ski goggles are not required for children, but sunglasses that block UV light are essential.
