Not sure I can answer it without making it worse.................LOL
the 22 films you are referring to belong to the MCU , which stands for Marvel Cinematic Universe
but not all Marvel movies belong to the MCU
it has to do with character movie rights
The X-men and the Fantastic Four movies have nothing to do with the MCU
both you and your grandkids are both right
yes , most all the 22 films are independent story lines of each other , meaning , you don't have to watch Iron Man 2 to know whats going on in Captain America 2
but........
think of these 22 films as a sound wave
there is a common theme thats runs through all of them , which is basically the Infinity Stones , but all the solo films self contained stories ,
and all these characters know each other , and even interact with each other in their solo films , not all at once mind you
some more the others , like Samuel L Jackson's Nike Fury , he shows up in just about all the 22 movies , not ever single one , but just about.....lol
but like Iron Man will make a guest appearance in the Spider-man solo film , and the Hulk has a good size appearance in the last Thor solo movie
alot of the movies will reference characters and events that happened in other movies
below is the list of the 22 films we speak of
notice , no X-men movies , no Deadpool and Wolverine movies , no Fantastic Four movies , or even the first 5 Spider-man movies
those movies are owned by different movie studios and having nothing to do with the MCU
The MCU films are the ones produced by Disney