Dear Fa,
I don't have to cancel until 48 hours ahead, so take your time, but personally, I think you would be better off with the earlier reservation with those little kiddos. You can enjoy the games (maybe assisting the little one), eat a leisurely and long dinner, then step outside for the shows-I guess there is a beach there.
Are you staying onsite? We did a trip 2 years ago and found it was REALLY nice to be able to go to the room in the afternoon and take a nap, then we hit the pool for a while, and then returned to the park. And remember, you won't be able to do it all-just enjoy what you do. The first time I went to MK with my son he HATED the rides (age 8)-so we just walked around and listened to bands and ate snow cones-it saved the day. He preferred Gatorland to Disney! My daughter, by contrast, is a true Disney fan-she is making lists and everything.
I'll wait to hear from you-I had discussed this with my husband also-we just figured that rushing from the airport to a dinner reservation was stressful and silly. I hope to visit WDW on a fairly regular basis, so we just do a little each time! I won't feel bad if you don't want it-someone out there will get it!
Janet, shivering in Michigan