The entire thing feels a little off because from the moment you learn how innocent children are from a group of murderers, you get this gnawing feeling you're just being tricked into caring for something you're told to care for. We all know Thanos is a terrible person before but you still need that extra gut punch to hammer it in. Sibling rivalry, wanting a sister, yeah, it makes sense but it was never earned because of the trickery.
They're Ravagers: pirates, thieves, murderers, kidnappers, etc. BUT they don't harm children. It's a lazy trope that deserves ridicule. It's what undermines some of the core themes of the movie because a seed is implanted the moment Stallone says the line.