Stuck in the Video Game: Between the Friendly World and the Apocalypse

Getting stuck in a video game without being able to get out of it is already a big challenge. But what if the difficulty level changes every 72 hours?
A teenager or even an adult deprived of warmth and love in our reality is by chance reincarnated with all his memories in a new fantasy universe. Here he is forced to play the role of a child slowly getting used to the differences between the worlds and finding true happiness among his new loving family.
We have all seen many examples of this and similar stories. But what if, for some unknown reason, fate has chosen neither a teenager nor an adult, but very young children?
Would a 5-year-old boy and a 9-year-old girl trapped in the body of a fox monster be able to adjust to a new video game reality with no way out? Will they find a common ground with each other despite all their problems?
But don't worry about them too badly! They found themselves in a friendly world with a handy Little RPG system...
Aw, oops... Who the hell changed the difficulty level? Why does this game world suddenly change to its apocalyptic version?