So the full itinerary (well, some parts tentative like the Grand Canyon) is this:
Quite frankly, this sounds like a complete cluster, especially with two young kids in tow.
You're driving xx hours to Vegas, spending just 1 night, then driving 5 hours to the campground?
Staying there for 2 nights, then a 4 hour drive to another campground, where you're spending just 1 night.
Then pack up to go to Vegas (again) for just 1 night, then drive xxx hours back home?
That's a total of 4 hotels/campgrounds during a 6 day vacation.
The vast majority of your time will be spent driving, checking into/out of hotels, and setting up/breaking down camp.
As soon as you get unpacked/settled into one place, it will be time to pack up and head to the next.
I would seriously simplify your itinerary, particularly with a 3 and 5 year old kids.
Stay in Vegas for 2-3 nights, then pick one campground to stay.
Or better yet, rent a nice VRBO to stay at the entire time and take a few day trips (Vegas, Red Rock, Hoover Dam).