I'm so glad that you have had a chance to ponder this more and have your 9 year old read the samples. I'm thinking, from what you've shared that it would be good to place your 9 year old in Preparing Hearts. Your 11 year old could also do Preparing Hearts and use the extensions and have a higher level of the 3R's. I'm leaning toward Preparing Hearts because I feel that while your 9 year old may be able to get by with the readings and requirements in CTC, I'm concerned that it may be too difficult for him in the long haul once you get to RTR on up. Placing your 9 year old well, will keep you from having to go back a guide with him later. Plus, it is easy to move a child ahead if needed, like your 11 year old, but harder to move a child back (as you then have to come forward again and run into a guide the child has already done).
Blessings,
Carrie