This story is available in the drabble collection, All I Want For Christmas.  

Bentley was thrilled with the personal Christmas present his parents had given him this year.  It was the ultimate gift, a real display of selflessness.  He sat in front of the tree, playing with the fire engine, making siren noises through pursed lips.  Yes, this Christmas was completely different.  Usually, at this point, most of the gifts had been broken, breakfast was thrown against the wall, and his parents were screaming at one another. Bentley began to hum ‘O Christmas Tree’ as his father lay sprawled on the floor and his mother swung gently on the rope behind him.