Thank you all so much for your suggestions - they were all so helpful. I wanted to follow up to let you know what we decided:

For the 12 year old boy:
- Winter coat (on his wish list)
- Books: Guinness Book of World Records 2013, The Hobbit, and Calvin and Hobbes: It's a Magical World
- Toy: K'nex Double Shot Roller Coaster

For the 11 year old girl:
- Winter coat (on her wish list)
- Books: Kate DiCamillo Boxed Collection (Because of Winn Dixie, Desperaux etc), MindWare Color Counts Landscapes with colored pencils, and The Happiness Project 5 year journal (with Smencils)
- Toy: Bop It XT and American Girl Crafts Mirror Message Board Kit

I hope they enjoy the gifts!