I'll admit I haven't seen the current Star Wars nighttime show in real life, but I LOVE Star Wars and was blown away by the previous Star Wars fireworks show (Symphony in the Stars). The current one, at least via Youtube, just doesn't impress me as much. But I'm not a fan of all the projections of movie scenes. I've seen the movies, I don't need to re-watch scenes from them on the front of a building. I much prefer full-on, in your face fireworks set to the iconic Star Wars score. To me, that show was impressive whether you liked Star Wars or not. But if you're not a Star Wars fan to begin with, I'm not sure the current show would hold much appeal since so much of it is projections of scenes from the movies.
Thus ends my thesis on current Star Wars vs previous Star Wars nighttime spectaculars, LOL!
As for the others, I saw Fantasmic 17 years ago (and have re-watched it on Youtube). It was okay, but I think we had crappy seats and it was cold and had been raining that night. One thing I do read on here is that young kids can get frightened during this show because Mickey is battling villains and some parts are "scary".
I freaking love IllumiNations, but it doesn't feature anything overtly "Disney" since it's basically a show about world peace. It's beautiful if you've got a good vantage point (I'm one of the weirdos that gets a FastPass for it, but there are lots of good places to watch from around the World Showcase). Like I said though, maybe not the most appealing to kids.
I have only watched Rivers of Light on Youtube so far (hoping to change that in December!), and it looks pretty great. I think a plus for this one might be that if your little guys are at all scared by the noise of fireworks, this show doesn't have that element. And if they like animals, all the better. Still, it does seem a little "slow" at times, so they might either become bored and restless, or...fall asleep (which wouldn't be horrible, right?). This would be the "gentlest" nighttime show.
If Wishes were still going to be running, it would be my hands-down recommendation. As such, I feel like its replacement is probably a sure bet as well. If you're only going to see one fireworks show, make it the one that is going off behind the castle in that iconic Disney fashion. AND, if you don't want to fuss with the mobs of people in the Magic Kingdom who will be watching and then trying to exit when the show is over, you can always watch this show from outside of the park at either the TTC or one of the monorail resorts.
As for HalloWishes, I haven't seen that one yet, but I hear it's pretty great. No idea if there is a "scare" factor involved with it, I assume it focuses on spooky and villainous music and voices, but that might not be so bad.
I say watch them all on Youtube and decide which one you really want to see in person.