That should be fantastic. I can't wait to see your trip pics.
How long are you staying at Zion? Where do you like to camp there.
If you like the scenic small roads, the eastern exit from Zion is amazing. You'll probably have to pay a few extra dollars since you're oversized, but you get to feel like Mr. Important when you drive down the middle of the lanes and they stop traffic for you. Checkerboard Mesa on the other side of the tunnel is gorgeous and the drive north on the 89 is more interesting than the 15. Either way is beautiful though.
Have fun making memories. Your kids are awesome.