Since your kids are so young, I would not plan an ADR that first day at WCC. I would plan an ADR at MK - maybe Crystal Palace with the pooh characters - and then spend time at MK. That would save you from having to get from your hotel to WL and then from WL to the park. You coould just go straight to the park from your hotel. We are doing a similar thing on our trip. Arriving around 3, reservations at O'hana's at 6:30, and then on to MK. I'm not sure I would do it if my kids were young.