Yeah, and on top of that, the promo video that the Steam store page has for Undertale promotes it as the "RPG where no one needs to die" so that's already giving you a big clue besides what Toriel tells you in the very beginning.

Although I'll admit...

Spoiler:
I spent a REALLY long time on the Asgore battle the first time around thinking there was a way to talk him out of it but you do have to fight him a little bit. And the Undyne battle was a bit of the same, didn't really think running away was the only non-violent option until I realized giving up on talking her out of it and just running away from the battle was the solution.