Making games to play with yourself is the art of playing. When I am bored, I make some slime and squish it with some chemicals and do experiments or while studying, I act as if I am a teacher and teach all concepts to imaginary children and sometimes to my parents too!
Totto-chan had a pet. A pet comes with a lot of responsibility, but you always have a partner to share your feelings with. I sometimes wish I had a quiet puppy, but I am not ready to take the responsibility, and I think that if we keep a pet, we shouldn't keep it in a cage and bring it with its sibling or mother, so we don't separate the pet from their family.
The innocence of a child is all about their selfless compassion - In Japan, they call it - Omoiyari, a section of Ikigai. In the chapter, even though Totto-chan was bitten by Rocky, she cared even more and ensured he wouldn't be scolded.
Selfless compassion was mastered by Totto-chan at such a young age. But as we grow, we often start to think more about ourselves and not about others, but I bet when Totto-chan grows up, she will have mastered Omoiyari!