There are ways undertale feels geared toward the way a kid sees the world (primary conflict being familial + focused on extrapolations about adults in your life, you learn to be nice) and deltarune feels geared towards growing up from that and the ways one thinks as a teen (primary conflict involves who you are + the influences of friends as new primary others, you learn that while you should try and be nice there are situations where you have to fight back). Just thoughts!