Spy Kids 5

Spy Kids 5 was supposed to be the next entry to the original Spy Kids franchise, following Spy Kids 4: All The Time In The World. It was supposed to include "5D", as the next step after "4D" was in the fourth film.

Plot
Unknown.

Why It Was Cancelled

 * 1) The main cast were too old to reprise their roles. They were also pursuing other projects.
 * 2) Spy Kids 4: All the Time in the World received very negative reviews.

Results

 * An animated reboot known as Spy Kids: Mission Critical was released on 2018.

Source
https://spykids.fandom.com/wiki/Spy_Kids:_All_the_Time_in_the_World#Cancelled_2013_sequel_and_later_plans