Don't know how long your trip is, but if your plane gets in at 1PM it will probably be close to 2:30 before you get to the hotel and get checked in. Assuming MK and MGM will close fairly early that day I would be tempted to just go to my room, unpack, let the kids explore the hotel (it is SOOO cool) swim if it is warm enough, maybe even rent bikes and ride over to Ft Wilderness or ride the boat over there and do the petting zoo, see the main st horses, etc. Then you could have an early dinner at WL or Ft Wilderness and crash fairly early. I love our arrival days... everyone is so happy to get to WDW and the WL is so neat, especially in the cooler months...it is always a joy to just settle in and enjoy the resort.
We always seem to be tired early that first day (everyone was always so hyped about going)...and it is nice to not feel like we need to rush off to a park right away....besides I am usually too cheap to spend the $$ for a day of park tickets when we might only have 3 or 4 hours in the park.