It's an interesting idea! It's not currently possible in Q2A though you're welcome to make a little add-on that does this.
You could do it at question display time (at the end of qa_page_q_load_q(...) in qa-page-question.php, set $question['selchildid'] based on the $answers).
Or you could actually have something running in the background which looks for questions of a certain age and then sets the selection permanently by calling qa_question_set_selchildid(...) in qa-app-post-update.php.
From the users perspective the second method would actually give points and send a notification for the selection, whereas the first would not.