Check out Winter Park for the snow activities. The Colorado river is nearby and the Williams Fork tailwater flows into it near Parshall. The water is usually open there at that time of year and there is some decent fishing. The fishing sites are not especially scenic, but it usually fishes well.
Another possibility is the Eldora ski resort near Nederland, west of Boulder. This is a smaller resort and tends to be a locals place which also means it is less expensive. South Boulder creek, below the Gross reservoir dam, is usually open water then. Smaller trout, but more scenic. Boulder creek, which runs next to the road between Boulder and Nederland, will probably also be open. Your family could use Boulder as your base camp for the trip as there is more to see and do than in Nederland and, with CU out for the winter break, it won't be too crowded then.
Estes Park doesn't have a ski resort but is in a spectacular mountain valley and there should be open waters nearby. The Eldora ski resort is not too far away and the town is next to Rocky Mountain National Park. It is a tourist town in the summer, with lots of lodging options, but my impression is that the crowds die down in the winter. I also suspect there are places there where the locals go for sledding, but don't know this for sure.
Thanks for your service! Wherever you end up going for this trip, I hope you and your family have a wonderful time. You ALL deserve it!
Brad