Children can understand an explanation without being ready to feel differently.

Understanding and feeling settled are separate arrivals, and they do not come at the same speed. A child can repeat the reason perfectly and still be frightened, angry, or unwilling, because the explanation has reached one part of them and left the rest untouched. Explaining again more slowly rarely helps; what is needed is time and company rather than better information.

Say the true thing simply, once, and then be available. Let the same question be asked again next week without a sigh. Being allowed to feel out of step with what you understand is most of what helps.