=Min(Children()) not consistently updating for parent row


I am trying to create a column of "Next Action" which will have a date for each row that is manually updated continuously.  I want the value of this column for the parent rows to update according to the next/oldest date (whether the furthest in the past, or the closest in the future) of the respective children rows.

I have been using the =MIN(CHILDREN()), which works one time, but then when I update a child date, the parent date does not update.  

Thank you for any help you can provide.