December 2024 we took extended family on a MK firework cruise. Total of nine people including my two granddaughters ages 3 1/2 & 5.
Like you, we gathered as much information as possible beforehand. We prepared the girls that they would have to wear life jackets and the cruise would last 1.5 to 2 hours. I don’t know what happens on the Epcot fireworks cruise, but for the MK cruise we left GF and traveled around Bay Lake & WL area and then parked for the fireworks.

They loved it! The whole family loved it. This is on our must do again list.
Best to be prepared so bring the noise canceling devices.
Go Noles!