Hey, Linda! We're back from convention, and I'm just popping in to catch up on the board! Thanks for your patience.
As far as your kiddos go, they fit right in with the target age range for Preparing... (which is age 8-10 with extensions for ages 11-12). After viewing the samples and the books at convention, we have many moms choose to use Preparing... with even older students. They are just thrilled with the content and the design of the program.
From our perspective, it is easier to beef up a program than to water one down. So, if you had a specific area that you wanted to add to, it would be easy enough to do (especially since Preparing..." is on a 4-day schedule). For example, on our 5th day this year my oldest son did a computer curriculum, Shakespeare, art study, a hands-on history kit, and his nature journal. You could easily add your favorites on Day 4 as well.
You'll also want to make sure that you have the proper level of language arts and math. Drawn into the Heart.. would definitely be enough for your literature study.
As far as the extension pack goes, the schedule recommends twice weekly written narration, twice weekly oral narration, and once a week a notebooking entry of the child's choosing. This is very Charlotte Mason in its approach and is what we use with my oldest (whose going into grade 7). Only you can tell whether HOD fits your philosophy.
If you have other questions, ask away!