You guys are selling children short. I work with children everyday and they are capable of so much more than most adults give them credit for.
I'm involved with the Cubs with my son and he started as a Tiger last year and he and his den had no problem knocking out the objectives in his Tiger book. There is a Scout Handbook for each level and is geared accordingly. I assume your son will be in your Tiger Den so he will need a Tiger Handbook, if your Pack doesn't provide it go to the local Scout store and pick one up. There should also be available for you from the Pack a "Cub Scout Den and Pack Meeting and Resource Guide" which is a meeting by meeting plan from Tiger to Webloes for activities to get them through their requirements.
Set reasonable expectations for them and remember your not teaching children, they already know how to be children, your teaching growing adults so keep them challenged and see how they grow.