Thanks everyone for your replies - I had no idea my post would get so many people commenting.
This trip was booked a couple months ago, originally just for my mom and I. At some point one of us (my mom or I) will bring up the idea of taking the kids which is what happened this time as usual. I really think I'm going to take your advice (and my gut feeling) and just do a mom and me trip. And attempt a stay at the Beach Club - now that's a vacation! On top of that, I sometimes think that the kids have been too many times and it has lost the specialness for them, if that makes any sense. And they better appreciate it because eventually, I plan on having my own babies and taking them to WDW - there is no way I'll be taking my kids plus someone elses!
And if the time comes at some point for us to do a short trip (since we are 2-3 hours away), and we want the kids to come - I will definitely kindly ask if they could contribute to the tickets or something, assuming its not a special occasion (like their birthday - one year that was their gift - a weekend at Disney). And if they say no, then I guess no more disney for them until their parents take them - which will probably be never. They have come a couple times with us, for very short trips (like, 2 nights) and usually have fun but the idea of going there year after year, or even for more than a day or so is completely lost on them. They just don't "get it". And that's okay - they accept that "I do".
Thanks again for all of your replies and thoughts!