I'd say that when a question from a child is called "stupid", it's more likely that the grown-up is the stupid one.
Children can ask hard questions sometimes, and grown-ups can get embarrassed when they don't know the answer. Instead of admitting their limitations, many adults will call the question "stupid" or the euphemisms "funny" or "strange", indicating that the child should not ask such difficult questions.
Children can ask hard questions sometimes, and grown-ups can get embarrassed when they don't know the answer. Instead of admitting their limitations, many adults will call the question "stupid" or the euphemisms "funny" or "strange", indicating that the child should not ask such difficult questions.