Not to add to your panic, but you do need to plan!
Don't know if you are staying on property or not, that can make a big difference.
Hopefully you have made ADR's (ressies) for any sit down restaurants you would like to go to. It is actually quite late for that. Do not expect to be able to walk up to any sit down restaurant.
With the small children, you will have your visit somewhat restricted unless you want to do parent switch on some of the more adventurous rides. I suggest start the day early, head back to your room for a nice nap, then venture out for dinner and some evening activities.
With the small ones, your pace needs to be nice and slow. Take your opportunity to stop and smell the roses.
Mostly, don't overthink it or you will not be able to enjoy yourself.