Book 9 is basically a review book in that it does not add any new sounds to our repertoire.

However, comma.

Book 9 requires the child to be able to read the number symbols 1 through 10.

Depending on the age and readiness of your child, he may or may not already know the number symbols. Knowledge of number symbols, though important, is not prerequisite knowledge for reading (contrary to the belief of text-messengers everywhere).

There are a few options if your child does not yet know the number symbols. The first is to read through the book with your child reading words and you reading number symbols. The second is to stop now, teach the symbols, and return to reading in a week or two (not highly suggested by me, by the way). The third is to skip the book and come back to it.

I personally would choose either the first or third options. Either way, if your child is beginning to read, he is perfectly capable of learning the number symbols, so get a puzzle or (my personal favorite) a piece of paper and some blocks to count, and start teaching those symbols. Once your child has learned the symbols, even if you choose option one and read the book right away, go back and read it again, letting the child read the numbers alone.