I think staying in Seward is a great idea. A rental would give you the most options to stop along the way from Seward to Anchorage, if you could find a vehicle to accommodate everyone and luggage. The kids would probably love the Alaska Wildlife Conservation Center. There are occasionally dall sheep at Windy Corner at Mile 106 that you could stop for. Sometimes beluga whales in the inlet and if you’re timing is good, the bore tide is a neat experience watching the standup paddle boarders ride the wave. You’d hit Potter Marsh and the boardwalk just prior to getting to Anchorage.