One thing kids can learn is that some kinds of writing require that specific conventions are required. A letter, for instance, has five parts: the heading, the greeting, the body, the closing, and the signature. Understanding that writing has conventions that should be followed will help them throughout school.
Another thing kids can learn is the concept of "audience." We don't write the same way -- or we shouldn't! -- to everyone. Writing to Grandma or Grandma is not the same as writing to our best friend. Writing to a best friend is not the same as writing to someone we just met.
This is a great time of year for kids to practice letter writing. They can write to grandparents, wishing them a Merry Christmas, Happy Hanukka, a happy holiday season, or a Happy New Year. And since kids tend to be home from school for winter break, it's a great time for them to find a pen pal.
The best part about writing letters to a pen pal is that if you find one from another country, you get to learn about a different culture! Here are some websites that help kids find pen pals:
Pen Pals for Kids
Amazing Kids (requires a small registration fee)