“Time Rules” have already been “broken”.
It’s very clear Characters are being pulled from multiple points in their timeline.
Examples:
Syndrome is alive, but the Parr Family are aware of the events of Incredibles 2. Joy mourns for Bong Bong in a friend campaign, but he is mentioned to be alive in a friend mission. Kevin Flynn has experienced Tron Legacy, but Tron himself has not.
There are many more of these, but those are the most memorable. My point is it wouldn’t be breaking any rules if Kion or Sofia or Jake showed up. They still shouldn’t though. The game has marketed itself as a 10+ kind of game, while Disney Junior is for 3-6 year olds. It would clash with the tone of the game, and bring in players far younger than should be present.
Badges, and mentioning in friendships would be fine.