If you plan AK, plan to see Lion King (use a fast pass for it and try to sit in front) and Finding Nemo. Both of these are theatre events and provide nice downtime.
The Safari is not on your feet either.
If grandparents are struggling, maybe let them take a break while you guys do the boneyard. They can sit while he plays.
The evening entertainment there (Rivers of Light) is not heartbreaking if you miss it, so it could be a much shorter day.
I assume you are not staying at a Disney resort, so going back to your room midday is not a really viable option.
Plan to eat at Flame Tree Bar B Cue, excellent food and HUGE portions. You could definitely save $$$ here by sharing a meal. (And believe me, they are sharable).
Enjoy your time, it's a great park!