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I would put both children in a group with 'submit' permission and let them post what they like. It's no fun to have to wait to have posts moderated, even for adults.
If you then put the other dad in the 'Webmaster' group and asked him to subscribe to email notification of new articles, either you or he could log in and edit/delete anything objectionable.
Or, each dad + child team could agree to share the same password so dad could always edit the articles if needed. Of course, your daughter could change the password, but I think even an eight year old could predict their parent's reaction to doing that!
The News module has a separate 'Submit' permission for specific user groups.
A thread is for life. Not just for Christmas.