MRS. MICKELSON AND TOOKIE   Mrs. Mickelson didn't mind holidays alone.  No tree.  Yet a wreath on the door, a creche on the end table and the army of cards that marched across the buffet, their cadre added to daily, signified her simple assent to celebration.    This year was different.  Everything piqued her tears:  thoughts of Christmas past, carols, even seeing or hearing children on tv, simply  looking at holiday-lighted windows.    Through one of these tears, she looked at Tookie, the little latchkey kid across the hall who let himself in and didn't come out 'til his momma got home, like it was the first time she had ever seen him.    Mrs. Mickelson overheard Do you have to work on Christmas? and noted the disheartened shrug of the boy's bony shoulders, the blank look of benign acceptance, that overtook his eyes as he softly closed the door behind his momma's nodded "Yes" when she left for work one morning.      Mrs. Mickelson was surprised to hear herself say can Tookie spend Christmas Day with me?  Sure -- okay with you, Tookie?  Tookie nodded his head yes while the same disheartened shrug and blank look manifested for a moment.    On Christmas day, side by side on the sofa, Mrs. Mickelson and Tookie watched the parade.  She showed him her scrapbook of Christmas Past in her snowblown hometown.    Tookie attacked the stuffed hen -- More dressing -- more mashed potatoes?  Mrs. Mickelson cut two pieces of red velvet cake as she explained that she always baked a cake on Christmas to celebrate a special birthday.  Tookie agreed with her observation that the cake couldn't hold 2005 candles and laughed as the thought overtook him.    Mrs. Mickelson moved the next February to her nephew's house in Braeburn, Texas.  Tookie was run down in April by a surprised driver who didn't see him in the dusk-light.  Tookie died two days later.    When Momma went through his things, she found a name in his notebook written in red with the fancy script that all kids seem to try out when they learn to write cursive:  M R S    M I C K E L S O N.  It was enclosed in a heart.