Answer about French language: not only this particular use of tu and vous is not standard, it just is not relevant. For the usage of tu and vous, see, for instance, this site or wikipedia. The app could use tu or vous, question of choice on what they want to convey, but definitely the same form in both, correct and incorrect cases. In educational contexts, tu will be used most of the time, chiefly with younger children. I expect most teachers up to upper secondary level will say tu to their students, the use of vous (at least in France, I can’t speak for other French speaking countries) would convey a special meaning of some sort (e.g. to show respect)*.
From a learning point of view this app (here representing the teacher) might hinder the kid’s future learning of the language, by confusing him about the usage between tu and vous. Whereas in some situations between natives (or with proficient learners of the language) one could play on the use of tu and vous to convey a feeling of some sort (anger, irony, etc.) it would be non pedagogical with someone starting to learn and not able to understand the subtleties of the language.
(My advice: find another app)
* Famous paediatrician Robert Debré would say vous to his young patients, thus breaking with traditional conceptions in medicine and psychology and wanting to show that infants and children were people, just like grown-ups.