I can't tell you about any plans, but I doubt birth dates would be made publicly available. This is especially true for children since youth protection is such a high priority. I can see birthdays (day and month) being added at some point. Just to satisfy privacy concerns I would think the visibility (privacy) option default would be private.
JD Lessley
Have you tried finding your answer on the ChurchofJesusChrist.org Help Center or Tech Wiki?