The aunt is a kill-joy, a spoil-sport. We are not told this directly, but can infer it from her of habit of devising 'treats' for the children, for the sole purpose of excluding one or all of them as a punishment. She presumably does this in order better to assert her authority. From a child's point of view, she is an infuriating grown-up - she often doesn't listen when the children tell her things, and changes the subject when challenged.