The story takes place in an alternate reality from the rest of the Sailor Moon series, so it does not fit to the main storyline or canon. One of the main reasons it does not fit into the main storyline is because it is stated in the main series that Usagi Tsukino will only have one child (Chibiusa). However, the lead character created especially for this story is Usagi's second child, Kousagi Tsukino. The daughters of the other four Guardian Senshi (all in grade 3 with Kousagi) also are in the story, who look exactly like (and are named after) their mothers (though the Japanese spelling of the names are different).

(Source: Wikipedia)