I booked some flights to DEN for Thanksgiving with use or lose vouchers hoping that there might be enough snow to ski. We were planning to go to Keystone, and while it's already (partially) open the base is still pretty thin.

Are there other family-friendly recommendations up to about a day's drive from DEN? Maybe hot springs/indoor waterpark resorts? Appreciate any tips.

Rocky Mountain National Park. It's about 90 minutes from DEN and has plenty of non-skiing stuff to do. There's more advice about it here:

Visiting the Rockies over New Year's Eve

Skiing around Thanksgiving is always hit or miss. If you still want to ski, keep an eye on Arapahoe Basin. It's 15 minutes from Keystone and traditionally opens earlier and gets more snow. Also keep an eye on Loveland Pass Ski Area.

If skiing is out, take a look at the Winter Park / Faser area. There's usually a lot happening there. The snow tubing hills are a heck of a lot of fun. There's also a hot spring resort, Hot Sulphur Springs 40 minutes away (never been).

The snow tubing hill in Fraser that AMflier mentioned is fun and they have snow machines in case there isn't enough snowfall for tubing.

Edit: change the text after AMflier beat me to it re:tubing hills.

And if you're a beer person at all, Breckenridge is another cool mountain town and they have the Breckenridge brewery down there.

There's also the town of Evergreen with a lake. I've never been there during cold weather, but I reckon it'll be picturesque during this time, especially if there's now.

And there's a nice German market in downtown Denver that pops up every year:
https://www.denver.org/event/christkindl-market/68496/

And you can ice skate in downtown if you're into that.

you can day trip to vail and breckenridge

about 25 yrs ago had a family reunion in that area over thanksgiving. Skiing was open. It started to snow the weekend before. Thrn it’s so hit and miss.

next week forecast across the country has milder weather.

You could always day trip it to Glenwood Springs and their hot springs. Fair warning: I would bring swimsuits you wouldn't mind throwing away after use, as the sulfur content in the water can be difficult to eradicate.

My wife and kids went skiing at Keystone on Monday. They said the snow was okay. But, yes, will definitely be hit-or-miss around Thanksgiving.

Thank you all for these helpful ideas. I'm keeping my fingers crossed that Keystone will get a little more snow. There seems to be people lining up for the lifts when I check the live cam from time to time. Tubing, hot springs, and a scenic drive are great alternatives.

Vail is set to open this weekend. They have a fairly extensive snow making network to help supplement the natural stuff. I skied Keystone 2 weeks ago and it was just ok. Not much of the mountain was open and they haven't had any significant snow in the last 2 weeks. The lift lines were out of control (blamed on short staffing and limited open terrain).

Happy to report that the day before we arrived, DEN received about 14 inches of snow. Thanks, bomb cyclone! According to the Keystone website, only about 7% of the trails were open but it was certainly enough variety for us to get in some decent skiing. We had a little bit more snow on Black Friday but then it got windy. The mountain was pretty empty with very short lines. Often we could ski into the line and be next for the chair. It may have been bad/early conditions by CO standards, but it was better than the best day we could have in the small hills in PA outside of the DC suburbs.

Maybe it's because I'm getting older, but I forgot how much the elevation zaps you the first couple days. I had planned to do a lot more but opted for nights in due to altitude headaches and the dryness of the air. Overall, a great getaway.

The cure for altitude headaches is water. Then more water. And water on top of that.