Dates are important in AK as our summer is short and what you can do/see varies from beginning of summer, to its middle and its end.
Do you your travel dates yet?
As mentioned, basing out of one place is not necessarily good because of the great distances between places. You could use Anchorage for a couple of days to visit Girdwood/Portage (though I'd be more tempted to look for rental accommodations in Girdwood instead). Then move on to Denali, Seward, Homer, etc. to visit those areas.
I love the Girdwood/Portage area. I also think it's one of the best places for families. I've listed a bunch of things to do below (with links). I find Byron Glacier & the hand tram at Winner Creek especially good "value" for effort.
Here's a google map link to give you an idea of where the are at:
- AK Wildlife Conservation Center (wildlife)
- Crow Creek Mine (historic and pan for gold)
- Crow Pass (adventurous hike)
- Winner Creek Trail (awesome hand tram & gorge)
www.alaskahikesearch.com/Hikes/Winner.htm (start from the "mine" end)
- Byron Glacier hike/walk (play on the toe of a glacier - keep a plastic shopping bag available for a sled)
- Portage Glacier cruise/boat ride
- Begich Boggs Visitor Center
- Whittier Tunnel
- Portage Pass hike (Whittier side of the tunnel)
- Trail of Blue Ice (Williwaw/Portage)
- Williwaw Salmon viewing (in season)