The problem you are running into has two faces, both of which are that you are not the target audience.

1. The first problem is that it is a very meta form of satire. It kinda depends on you having played enough rpgs to have internalized how they work. The idea that killing the various monsters and gaining Lv. is objectively bad will not hit you as hard if you are an outsider to the genre. There's also lots of other little details you will miss the meaning of, like how Toriel leads you through the spike puzzle because "its too dangerous".

2. Undertale has a lot of messages woven together in its themes, but the loudest and clearest ones are "Your actions matter, even if nobody notices" and "People are fundamentally good, and you can make friends with anyone if you try hard enough". I don't imagine those are messages you need to hear, since you are an adult, but when I was in school I did not feel like I mattered. School is a rough place, and I think your kids really appreciate being told they matter and that they are loved.