Trust.
The backbone of relationships: romantic, platonic, or otherwise.
Trust does not come easily but it can be destroyed in seconds.
Trust can be as powerful as love and hatred, yet it is rarely acknowledged as such.
Trust was another aspect of life that Rosalina had tried to teach the Lumas about. An important one, it was a big reason why they were even a family at all; the Lumas trusted Rosalina to look out for them and Rosalina trusted them to not make silly decisions (which they managed for the most part). Part of this lesson was to give them a taste of freedom every once in a while; let them explore, let them roam, don't fuss over them too much.
So that was why Rosalina was trusting a group of Lumas to play with the giant trains responsibly. Why she was trusting another group to visit the gizmo inhabitants without annoying them. Why she was trusting yet another group to try some cake - as well as the candy that decorated it- without ruining their appetites for dinner.
Rosalina sat back, chewing on the colourful coating of some hard candy, watching the Lumas sort out amongst themselves who should get what.
She couldn't be there supervising every single group. As much as she wanted to, she knew she had to back off a little bit, let them dip their metaphorical toes in the water of independence.
Of course, when they needed her help, she would rush over without hesitating. They were her precious little star babies, after all. She would not abandon them in a time of need.
And so it was that when several started crying over the unfair cake division process, Rosalina stepped in to settle the matter.
And when the gizmo people complained irritably about the Luma's squealing and noise-making, Rosalina told them to hush.
And when one nearly fell off the giant train, Rosalina swooped in and scooped him up.
It was still a lesson in progress, after all.