You’re on vacation. Sleep is always a priority!
Our first visit to WDW, our kids were 7 and 9. We showed up at rope drop and left the parks every day before 5pm, missing every single nighttime show.
And it was still a great trip! We didn’t feel we’d missed out. Our days felt jam-packed.
Yes, your kids might love Fantasmic. Mine did, when we finally got to see it on a subsequent trip. But, nothing at WDW is worth sacrificing sleep over. Better to be well rested and thoroughly enjoy fewer things, than to be exhausted and cranky trying to fit everything in, and end up unhappier in the end.