I am pretty new to bonsai-ing myself. However, are these trees pines and like outdoor plants? From what I looked up, they look like they are evergreens and outdoor plants. I would have placed them outside all year long, but since you have been growing them inside, just keep them inside.
I would grow the plants inside through the winter, especially since they are young. I would make sure they are mature enough to live outside. As soon as possible, put them outside to grow well.
I don’t know the climate of Missouri, but I know that MOST LIKELY, these trees are outdoors, so try to keep them outside.
If they are doing well, then just keep them growing inside I guess.