Lots of good advice here from seasoned travelers and past/present residents.
Your first glimpse of Alaska as you fly in if it's clear will be "holy******- It's big"......which is why the advice from those who've said go north or south but don't try both in 8 days is sound advice.
The least amount of driving and most amount of activities will be to go south to Girdwood/Whittier/Portage/Seward/Kenaii/Homer.
Please be very mindful of the traffic - you wouldn't think it would be a problem, but since we only have two seasons up here - Winter and Construction - there is a lot of competition for the (often torn up) roadways.
One last note - you can bank on the kids sleeping well when you finally get them to bed. You are here when it will still be light nearly 24 hours and it will be 10pm when you suddenly realize you need to start thinking about dinner!