The child asking again may be testing whether the answer is dependable.

Repetition is not always forgetfulness. A child who asks the same question for the fourth time is often checking whether the answer holds, whether you will give the same one when tired, whether the world is the kind of place where things stay true. The information was received; what is being tested is the source.

Give the same answer in the same words, calmly, however many times it takes. If the answer has changed, say that it has changed and why. Consistency is doing more work here than any explanation you could add.