It's not often a movie will get me to shed a few tears unintentionally, but this is one of those films that managed to do so.
As other reviewers pointed out, there is a thin line between disciplining your child and abusing them. The movie also threads over this topic ever so slightly along with giving a few scenes juxtaposing how parents need to be firm but also avoid stepping over the line. We get to see this in practice where the main character's nephew comes across as a bit bratty, and he at times will chide him. But then we also see what happens in the case of Da-bin and her brother, and how that wasn't just discipline but outright abuse.
The director did a fine job of pulling at the heart strings to force the audience into truly uncomfortable situations, which was highlighted by the excellent acting from the two kids. It really made you feel for them. Couple that with a moving soundtrack and well lit cinematography, and the movie gives you this contrast between what should be a feel-good experience and something truly heartbreaking.
This is a tough film to watch at times, and if you're not in the mood to shed some tears (no matter how tough you think you are), then you might want to go for something a bit cheery. Even still, this is a fantastic film, and tugging on the emotional cords of viewers comes naturally with the way the story unfolds, which makes it well worth the watch.