I'm not commenting on whether or not I think you should get your own checked bags. What I am going to do is try to convince you to pack your carry-ons with your immediate needs, especially the stuff for your kids' very specific bedtime routines.
WHAT IF THE AIRLINES DELAY YOUR LUGGAGE??? If this happens, your kids won't have their bedtime needs! If you pack the stuff in carry-ons, it never leaves your side, you don't have to trust anyone else to get it to you in a timely manner because it NEVER leaves your possession.
I don't understand why you find it difficult. For our first WDW trip, our kids were 5 and 2.5. They each had their own little backpack with jammies, bedtime buddy, swimsuit, change of clothes, coloring book and snacks for the plane, etc. Think about how very little space that takes up. And both of kids were very proud of having their own bags. The same held true last time when they were 6.5 and 4. That second trip was after the new liquids/gels restrictions. Just so you don't think I'm talking from the cheap seats without any first-hand knowledge ....
Each ticketed passenger is entitled to a carry-on. And each ticketed passenger is entitled to a 3-1-1 bag in that carry-on.
So no matter whether you get your own luggage or not, PLEASE strongly consider packing carry-ons for your immediate needs, anyway. You'll sleep better.