That is expected behaviour -
'Nested Pages', as opposed to normal pages, use 'weight' for sorting instead of 'date' and so there is no date field in them.
KK wrote: You can add a type 'datetime' editable region to the template.
If needed, it can also be moved into the 'Advanced settings' dropdown by customizing the admin screen - please see viewtopic.php?f=5&t=10241 for details.
Hope this helps.