Benjamin & Zachary have:

• The Hobbit (each)
• The Railway Children (whole series?)
• From the Mixed-Up Files of Mrs. Basil E. Frankweiler  
• A Wrinkle in Time (B)
• Island of the Blue Dolphins (B)  

Christian, Reilly, & Braeden have:

• A Wrinkle in Time 

List of titles to get them (or be sure they have):

• Ender's Game (B's 14? also C's 12th this year)  
• Treasure Island (Z?)   
• Copper (Z?) 
• Lord of the Rings 
• The Cavendish Home for Boys & Girls (NOT B/Z) 
• Jellaby
• Amulet book 1  
• Coraline
• American Born Chinese (C?) 
• Ladd Family Adventures (series) 
• Rick Riordan books (Percy Jackson & the Lightning Thief)
• Adventures of Tintin
• Lloyd Alexander's Book of Three series
• My Side of the Mountain
• Arthur, For the Very First Time
• Unclaimed Treasures  
• The Blue Sword
• True Confessions of Charlotte Doyle 
• Sounder 
• Year of Shadows  
• Beverly Cleary & Judy Blume books...?  
• Esperanza Rising (?)  
• Various art books: Maxfield Parrish, Frida Kahlo... 
• To Kill a MockingBird  
• Ember (?)
• Seraphina (?)  

Maybe in a few more years 

• Stardust
• The Princess Bride
• Jurassic Park  
• Eleanor & Park  
• Boxers & Saints 
• Maus 1 & 2  
• Eleanor & Park  
• Harry Potter (someday)  
• Hunger Games  
• Graceling series (?)