If a child tells you that they believe something very negative about themselves, that is a very important emotional truth to listen to! I think it's exactly this kind of dismissive attitude, which presents itself as common sense about the supposed irrationality of children, that is the problem. of course not everything anyone says is literally true, and of course kids have a limited vocabulary for what they are experiencing and may use metaphor, fantasy, hyperbole, and the like to get to the heart of a crucial truth that is not being heard. I am aware parenting is very hard and that deciphering meaning is challenging especially when the kid doesn't fully understand themselves yet either. But I think it has to begin by letting go of judgement and really validating those feelings and perceptions even if your adult lens may initially prompt you to not see it as valid.