The palace is big. She's lived in it long enough for her explorations to take her through almost all accessible parts of it, but sometimes years go by before she revisits a particular corridor. She chooses such an uncommon destination, unpopular because its doors are mostly locked. She taps them with her scepter, as she goes.
One of the doors has been left open.
She looks around. Heimdall sees all, but by default she isn't a tattletale.
She slips in.
"It should not have been," Odin growls, setting her down in the hall with a little shake and yanking the door shut behind them. "You could have died, girl. I have seen those who touch the Tesseract with their bare hands burn up from the inside. The artifacts of my treasure rooms are not a child's toys. Do not enter this hall again."
She leans into the embrace. "I went down the sixth floor west hall, the one with the room for all the old musical instruments that's usually the only thing open, and I was tapping my scepter on the wall, and one of the doors opened, and I went in, and there was a pedestal, with a pretty blue cube, and I liked it, and I wanted to pick it up."
"I'm okay," insists Loki. "It - told me things, I don't know how to say what things but there were a lot of them, and it put me on the floor, and I wanted to touch it again but Mother came in and picked me up by my tunic and put me out in the hall before I caught my breath, and she said I could have died, and to go to you."