From experience never use anything like stain and im assuming stripper in the house. Even low voc or whatever it’s bad. Especially when you got a little one. Made this mistake and couldn’t get it out to the garage fast enough. Never again.

Garage with a heater should be fine. Ive heard people build a little blanket fort for their piece to heat/cure/stain in by trapping hot air in there. Never done it myself and wouldn’t do it without constant supervision if you’re leaving the heater on.

One thing ive done is let the piece stay over night in the house prior to staining. Move to the garage and then stain. My piece usually retained heat long enough for the majority of the smell to dissipate. Using waterbase quick drying low voc stain in this case.

Sanding just wear gloves and your cold gear no biggy. Wouldn’t do it inside unless you got a space specific for this which doesn’t sound like you do.