Winterizing seedlings

I have several Pinus Aristata Seedling that are about 8 months old. They are strong and healthy and in individual pots inside my home in a sunny window. But winter is coming and everything I’ve ready about conifer bonsai says they do better outside during the winter. But these trees are very little and I don’t think they will survive outside our Montana winters without freezing. I was planning on keeping them inside for the first two years till they are more mature. But some books I’ve read said that keeping them inside messes up their normal dormant winter cycle. But I don’t have a basement or cool dark area to store them in that stays around 30-40 degrees for the winter. So I’m not sure what I should do with them.

These seedlings are not acclimatized to the outdoors because they have been kept inside.
Despite the normal advice and practice it is likely better to keep them inside for this winter if you can provide proper care to continue their healthy progress. The dormancy issue will not be a major concern for plants of this age. Good Luck

That’s kind of what I was thinking, but being new to growing bonsai trees or any trees in general I just wasn’t quite sure. And should I just leave them in the window where they are acclimated to the shortening amounts of daylight or should I put them under a grow lamp through the winter for this first year?

As they are indoors and the temperatures are conducive to growth, i would use a grow lamp and continue the growth throughout the winter. They will remain healthier that way.