You could provide evidence that the statement is outrageous or mistaken. Technically, the burden is on the parent to explain themselves, but that's always true

You could provide evidence that the statement is outrageous or mistaken. Technically, the burden is on the parent to explain themselves, but that's always true and readers are capable of assessing the comment and its (lack of) evidence without a content-free two-word demand from you. See Rob Aley's comment above for a better approach.