I cannot imagine taking a 3.5 year old cross country skiing. Downhill is hard enough at that age although completely doable. They just don't have a ton of endurance. The sled sounds very fun though. I would just plan on that.

They rent the a ski behind sled at Whitegrass for $5. You have to wait for the snow, check website. We put my child on skis at 6. We also dragged him in a sled (ski behind) for part of the time. He liked that, he is pretty light, but I think at almost 50 lbs this year (8), there is going to be no more pull behind sled.

Whitegrass has an awesome kids ski package which you pay once and upgrade until they are in adult sizes.
My son got one at age 7.

Whitegrass is nice. Could you tow a little one?

Been waiting to take my kids (ski camp, sledding, tubing, snowshoes) but not enough snow around here yet. When it finally gets snowy enough you might try the Davis WV area (Whitegrass Touring Center http://www.whitegrass.com/report.html)
Canaan Valley Resort & Blackwater Falls State Park have XC ski centers.
In Maryland they offer XC at several state parks
http://www.skisoutheast.com/activities/cross-country-skiing/maryland/
Seems young to me, I'd wait until they were older with a little more leg strength & stamina? I would call ahead to see if they can outfit a 3.5 year old.

My son tried both downhill skiing and cross country skiing at about that age. Downhill skiing was definitely easier. DH is a very strong XC skier, though, so he was able to pull DS around a fair amount, and DS enjoyed it. I don't think a dedicated XC ski trip would have worked well at that age. But if you are just looking to get a child comfortable in snow and on skis, however, 3.5 should be fine.

We've done most of our XC skiing in the West. But I hear that Vermont can be wonderful.

I think it may be too young, you have to have strong legs and be able to go distances, a 3.5 year old might tire quickly, like in the middle of the lake you're crossing .

But if you do go, Vermont is wonderful, definitely.

Cross country skiing requires natural snow - unlike downhill skiing where they can get by on manmade snow if it's cold enough. At this point you'd probably need to go to Colorado or Utah. If the weather starts to get a little more wintery around here then maybe Vermont, the Berkshires, or upstate NY. In this area it's really completely weather dependent.

My kids downhill skied at 3.5 but cross country actually requires a little more coordination so not sure if that works. Maybe others can chime in on that.

And is 3.5 too young for that?