I think we need to see a photo of the glass doors with the drapes open. Can't determine where to place furniture until the traffic pattern is visible.

It's hard to tell from the picture, but it looks like it is part of the kitchen. How about a kitchen table.

Judging by all the toys, I'm going to assume you are currently using this as a play space. So I would advise embracing that vibe:

A couple of low swivel chairs flanking the fireplace, facing into the kitchen.

Push the rug over so it is 18" from the wall. Add a short sofa, loveseat, or settee. Use the kids' table as a coffee table. Use a cube organizer shelf on the left side of the sofa to hold books, small ankle breakers, lego and a lamp.

Put the train table in the center of the room, or relocate it to a different space.

The fireplace is really pretty, now all it needs is some cozy seating for enjoying it :)

I would start with a sofa facing the fireplace with a sofa table behind it if there’s room. Add a grouping of chairs, all different but small, on the rug.

Turn the rug and do 4 small scale swivel chairs with coffee table in center and you can leave the children's area

I'd treat it as two separate rooms -- a couple of small chairs or ottomans near the fireplace for cold evenings, and then the rest of the room is a family room. Do you have a TV room elsewhere? You could put one on the far wall here, or just do as suggested above and make a comfortable grouping of chairs around a table (or a loveseat + two chairs could work). Maybe the kids get the middle zone for their playspace for the time being, or you slide the seating a bit toward the kitchen and put some toy bins on the far wall to catch the clutter when company comes.

If you turn the chairs so their backs are to the fire most of the time, you can push them right up to the hearth.

One would go almost in the corner formed between the stone and the wall, the other would go over by the window. That will leave you a clear walkway most of the time, and you can swivel to enjoy the fire and pivot back if someone needs to pass.

Exactly what I was attempting to describe! I think it would be so cozy :)