Last year we had family over and to get my then 8 year old daughter involved with the preparation I had her make placecards for the table.  It was really easy and she really enjoyed showing everybody her artwork, and she was able to make special cards for our family.  This is what we did.

We used business card inkjet paper - this way the paper is perforated and you can break them into two cards that can fold like placecards

We took crayons and colored pencils and drew turkeys, cornicopias (sp?), or little Happy Thanksgiving banners, she colored the pictures and the backgrounds with different colors for everybody then she wrote their names on the card with the picture.  Just one little picture on the side with the name.   Then I allowed her to decide where everybody was sitting.  She did a great job and was involved with our thanksgiving preparations.