So Yoshi's island doesn't really follow babby Mario and babby Luigi, it follows their clones. Bowser is trying to clone Mario and Luigi to take over the world, but then the Yoshis got him. Babby Bowser is just Bowser Junior from Super Mario Sunshine. Also the Yoshis can't talk so it's not like they can say "This is a clone of babby Mario and babby Luigi." Also this took place during a nuclear holocaust and also Bowser is the lost member of the teenage mutant ninja turtles and Princess Peach is an alien nazi.