Welcome to FT.
I I would definitely not try to drive from Denali National Park to Seward in 1 day with a small child. that goes double if you plan a stop in Talkeetna. also the best time how to make stops between Anchorage and Seward is on the way to Seward since all the pull outs for scenic views are then on the same side of the road.
be prepared to get off the shuttle bus in Denali if your kid gets tired or begins to act up. the bus driver will not stop for wildlife will leave the stop early if there's not absolute quiet on the bus.