Hey howdy hey Harrison and welcome to planDisney!
The nighttime shows in Walt Disney World Resort are such spectacular events, no trip to Walt Disney World is complete without seeing these shows. There are two in particular,
Disney Enchantment in Magic Kingdom and
Harmonious in EPCOT, that I strongly suggest everyone see at least once. Much like yourself, I have smaller kids and my wife and I often have issues being in such big crowds for the viewing of these shows. Especially now with Covid-19, this often can sway some differently with viewing positions of the shows as well. I can honestly tell you the first time that we did get to experience Enchantment in Magic Kingdom, it was not in front of Cinderella Castle. Instead, we were able to experience the show from behind the castle right by
Prince Charming Regal Carrousel. Watching the show from here, you get to hear the music and you are absolutely surrounded by the fireworks. They have some fireworks that are let off around Cinderella Castle but the big ones are a few miles down the road to help to illuminate the background at just the right height. At that vantage point, you are able to see so much everywhere you look that it is my second recommended location to experience Enchantment.
As of right now, yes the
park hours show that Magic Kingdom closes at 8:00 p.m. on March 8th however, keep checking back to the calendar as park hours might change closer to the date. Specifically to your question, no you do not have to be on Main Street, U.S.A. to view the fireworks at 8:00 p.m. You are also able to get in line for attractions around that time as the Cast Members will not let anyone else in line at 8:00 p.m. but anyone in line before that time will get to experience the attraction they are waiting in line for.
I hope this helps clear up the concerns you have about Enchantment in Magic Kingdom. One other thing to add on the location, where we were standing, there were people around but we had a ton of space compared to the wiggle room you may or may not get on Main Street, U.S.A. So grab yourself a treat from
The Friar's Nook or a LeFou's Brew from
Gaston's Tavern, find a nice spot to enjoy the evening and the show!
Let us know if you have any other questions!
Happy planning,
Nick