Hi Julie! True Confession time: I am not a fireworks fanatic. I know there are many people who wouldn't dream of visiting a Disney park and not staying through the evening fireworks show, but my family tends to value early mornings in the parks over late nights.
Illuminations: Reflections of Earth is a beautiful fireworks show that everyone should see at least once, but if your kids get cranky when they stay up late, you could skip Illuminations on this trip and catch it when they're a bit older.
If your little ones are night owls or huge fireworks fans, then it may be worth keeping them out one night to see Illuminations. There are lots of great spots for viewing Illuminations. My favorite way to watch the show is from a restaurant table -- consider making dinner reservations at Rose & Crown or La Hacienda de San Angel for 7:15 or 7:30 p.m., and request a table with a view of Illuminations so you can cap off your meal with the show. Standing on the bridge between the France and United Kingdom pavilions is another good viewing spot or if you're on the opposite side of the World Showcase, Norway has a nice view.
Once factor to consider is that you'll be caught in a large crowd leaving Epcot after Illuminations so returning to your resort will take extra time. Schedule your Epcot visit on the day before your rest day so you can let your children sleep in the next morning.
Thanks so much for visiting me here at the Moms Panel, Julie! Wishing you a magical vacation!