Lots of ski resorts promise free lift tickets for kids, but as we preach over and over, you always have to do the math to see if "free" really means free. Keystone Resort  in Colorado is offering a Kids Ski Free  package through April. Here’s how it works: Book a package that includes four weeknights of lodging in a two-bedroom condo and three-day adult lift tickets, and you'll get free lift tickets for kids 12 and under (one child per paying adult). The resort advertises that packages start at $229 a night, though that package rate goes up after February 11. When we test-booked the package for a late-January trip, here’s how it broke down:

• 4 nights lodging in a 2–bedroom condo at Evergreen Condos (normally $183/night x 4 nights = $732)
• 3-day lift tickets (for our dates, normally $231/adult x 2 + $111/child x 2= $684 for a family of four)

Deal or no deal? Alas, the kids aren't really skiing for free—the package just hikes up your lodging price to essentially cover the cost of the kids' lift tickets.  So forget the package. Your best bet would be to book a one-bedroom condo, which typically offer ample space for a family of four and a sofabed for the kids. For the dates we tested, one-bedroom condos ran $143 a night—which would bring your total spend for lodging and lift tickets to $1,256. That's 9% cheaper than booking the package, and 11% cheaper than booking a two-bedroom stay on your own.

No doubt about it, Keystone is laying on the kid-friendly fun this winter. The resort is hosting five different weeks of “Kidtopia,” during which you'll find a long list of activities (many free), such as “disco tubing,” glowstick ski parades down the mountain, live music, and sessions of arts and crafts. If you visit after February19, kids can explore the new Ultimate Snow Fort, which will feature a snow dragon, drawbridge, and lookout tower. And to sweeten the pot for any dates, Keystone will also toss in a free Adventure Passport, which gets you freebies or discounts on activities such as snowbiking, ice skating, sleigh rides, snowshoe tours and—especially nice for the parents—yoga classes and margarita, wine, or martini tastings.

The Kids Ski Free package is available now through April. Kidtopia dates are February 11-16 and 18-21, March 15-21, and April 1-6. Use the link when booking online, or mention Kids Ski Free when calling 888/222-9285.