Responses

That doesn't really matter. It would only add a few months to his age but this boy should be at least 5-6 years old.
Besides, that still wouldn't explain why she faked her own death. Her husband died/was killed and the crime scene was staged in a way that made it look like it a stranger did it. Which means that her husband wasn't a threat anymore and that nobody would've accused her. There was no reason for her to fake her own death.
Remember when the other policeman told Seungbae that Sangwoo's parents died 3 years ago? Even if we assume that about 6 months or so have passed since then that's still not enough time. Look at her boy. Does he look like he's at best 2.5-3 years old?
He can ski on his own. They went to the intermediate course. This boy is clearly older than that.