Since you pointed out that this is pretty much your "half-way" point (4 nights at POR and 4 at WL), I would use this as your rest day. Hang out at POR as long as possible- you won't have to be scrambling to pack the night before. I would get up and have breakfast, pack, do any laundry, etc (let the kids swim). Pack a small bag with swimsuits, extra clothes, etc and bring a plastic bag for wet things. Call bell services to pick up your luggage when it's ready and check out. Are you using Disney transportation to get to WL? Find out the easiest route . Check into WL- have lunch at Roaring Forks and explore the lodge!!!!! This would be the day to let the kids go wild in the arcade, if need be. I'm sure you will use the pool again!!!! After you check in and little one gets a nap , maybe take the boat over to the Contemp and have dinner at Chef Mickey's or stay at "home" and do Artist Point or Whispering Canyon.
***Another possibility is to ask "nicely" for a late check out at POR.
They may not charge you. It's not like "Tuesday" is a big arrival day or anything and this would greatly decrease your time "without a home". The worst that can happen is they would say no. Also, you can request for "early check in WL". there are no guarantees, but it never hurts to ask ...
Whatever you do, have a fun day!!!!