Hello Jennifer and welcome to the Disney Parks Moms Panel!
A day trip to the truly magical
Magic Kingdom Park does NOT sound crazy at all. In fact, I think it is a great idea as long as you plan it correctly.
My first piece of advice is to get there early. And by early I mean 30 minutes before stated park opening. I would avoid days with
Extra Magic Hours as resort hotel guests will arrive an hour before opening. Even if you are staying onsite, I recommend avoiding those days are there are typically busier.
My next piece of advice is to come to grips with the fact that you will not be able to experience everything the Magic Kingdom offers in one day. Make a list of your "must-do" activities and plan around those. For your children's ages, I would focus on Fantasyland- home to old favorites like Peter Pan's Flight, Dumbo the Flying Elephant, and it's a small world. You will also find newer experiences like
Enchanted Tales with Belle,
Under the Sea ~ Journey of the Little Mermaid, and
Mickey's PhilharMagic.
My final piece of advice is visiting touringplans.com. Those fine folks have designed effective plans for all types of visits to Walt Disney World. For a relatively small fee, you can even create a personalized plan centered on your must-do attractions.
I hope this is helpful for your magical one day trip.
See ya real soon,
Anne