I was standing in line at the post office when a sign caught my eye: "Operation Santa 2013." According to the poster, "answering letters to Santa has been a holiday custom for over 100 years." Those who wanted to participate could choose one of the many letters to Santa received by the post office and write back as Santa, sending the gift requested.

How cute, I thought. Kids request presents from "Santa," and they actually arrive.

I remember walking to the mailbox with my own letters to Santa as a child. One of my mother's favorite Christmas stories was how, when I was 4, I mistakenly threw my peanut butter sandwich into the mailbox instead of my letter. Santa brought me a whole jar of peanut butter that year.

I couldn't wait until my kids were old enough to write letters to Santa. Now they are too old for Santa Claus, and I miss him, so Operation Santa seemed perfect for me.

Bright and early on Dec. 3, the first day the program got underway, I drove to the main Los Angeles post office to choose my letter. I walked into a large, decorated room where Cleo, the "elf in charge," was waiting. I expected letters full of misspelled words and little-kid grammar, asking for Legos and Barbies, skateboards and My Little Pony. I knew there would be those who asked for phones or iPads or Xboxes, or other things out of my price range, but I figured I could find some little boy who still wanted a fire engine.

What I found were pleas from parents. A mother out of work said her family would eat, but there wouldn't be any presents. A dad wrote that his kids needed school supplies. Parents with two kids, three kids, maybe more, were hoping for help with what they couldn't provide. A dad just out of prison wanted to make Christmas special for the kids he hadn't seen for so long. A disabled grandmother asked for a church dress for her granddaughter.

I was overwhelmed. Many of the letters — even the ones from kids — asked for groceries and shoes, clothing and shampoo. One child wrote: "Please bring my mommy some food. She's been good this year."

Elf Cleo sat beside me at the table checking in a new batch of letters. She told me 90 percent of the Santa requests sent to the post office never get answered. Many are written at homeless shelters and city food banks and after-school programs. (I found one letter in which a young teenager asked for gifts for the shelter workers.) Cleo said that every once in a while a family's gift comes back unopened, marked address unknown. She wonders: Have they moved into a shelter? A car? Onto the street?

I read a lot of letters, and I felt worse and worse. I didn't know how to choose. The single dad who needed diapers? The 17-year-old asking for a backpack for her little sister? I believe in holiday magic, but there just didn't seem to be enough of it to go around.

I selected letters from two families, one with four kids, one with three. One of the girls asked for a truck for her little brother, who "make-believes our shoes are cars and trucks."

I'll send some toys, but mostly it'll be clothes and supplies and gift cards to grocery stores.

Nobody in the letters I selected asked for an Xbox, but I wish I had the money for one to send to the 11-year-old boy living in a shelter who wrote this:

"Dear Santa: I want an Xbox. I ask for it every year and I never get it. I guess I have been too bad."

Diana Wagman's most recent novel is "The Care and Feeding of Exotic Pets." She wrote this article for the Los Angeles Times.