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The 2 topics are not comparable, IMHO.
M22’s child is concerned about not finding a spouse for himself/herself, while your child is trying to clarify a rumor.
The general rule is that if the child is old enough to ask, then the child is old enough to get an answer on an appropriate level.
There’s nothing wrong with telling your child that it’s assur min haTorah, end of discussion. If a child cannot get an answer from the parent, there are other sources for the child to get answers. Better to get the answers from you.