Let them know how long it will take before they ask
Younger kids can't tell time, so let them know how long it will take with a frame of reference they'll understand. When our kids were growing up, if something would take a half hour, we'd tell them it would be as long as one Muppets program. Or we'll get there just before the sun goes down. You know what your kids will understand.
Create a relaxed atmosphere in the car
Bring a stuffed animal or blanket. Have some pillows so they can doze; they're more likely do sleep if they have something soft to lean against. Let them wear slippers or just socks in the car. Put a large pillow between siblings to help avoid squabbles. Put up sunshades on the side window to avoid glare. It also helps keep car sickness in control.
Stop and stretch
Stop every hour for time out of the car. Stop at a park or rest stop and toss a Frisbee or a ball, or even just blow soap bubbles. A 10-minute stretch will put everyone in better spirits.
Keeps kids occupied
Give your child a map with the route marked and help them look for road signs and follow the route. Give them a notebook to keep a travel journal. Bring some new games to play in travel sizes. On the right side of the page are a bunch of coloring pages from Crayola® you can print out for the kids. Bring crayons, not markers, because if you bring markers, they will get on the seat.
Talk to your kids
These ideas can help keep the kids occupied, but vacation times are times to make family memories. Talk to them and get to know them. You have a captive audience; make use of it. The memories are what you will all take away from the vacation.
If you haven't spent much time in the snow, here are some tips for dressing kids for snow play. They will be much happer, and so will you.
Dress in several thin layers
If something gets wet or if they get too hot, something can be removed.
Waterproof pants & jacket
These will let them stay out longer without getting wet.
Easy to forget, but very important.
Waterproof gloves or mittens
Keep their hands warm and they'll have much more fun. Knitted mittens are cute, but soak up moisture like a wick.
Goggles or sunglasses with UV400 protection
The sun is much brighter on the snow, and there is less protection at higher levels.
Helmet (for skiing, snowboarding and sledding)
Nothing more to say here.
Plenty of sunscreen and chapstick
Yes, you can get sunburned in the winter. And at higher elevations, you can get burned more easily.
Here are a bunch of pages to print for the kids to color in the van or in the hotel room.
It is not down in any map; true places never are.