Possible Clues:

• Sounds as if there's a berth here for a newcomer
• Ingenious to include four, then one more at birth
• With the Navy I get it up and down for Christmas
• Service includes it both ways for Christmas
• The arrival of a tiny one about five with it back
• Piero della Francesca’s example of this seasonal kind of painting is back on display at the National Gallery after a recent restoration
• Often seen at play in midwinter
• It was witnessed by distant kin of 18
• and 20 Across: Stable environment in a city 9 ultimately destroyed
• Biblical birth