I got my kid on Gcompris when she was 2.5 year old, and noticed a lot of rough edges UX wise. Small things on how feedback was given to a kid, or the lack of separation between games depending on how suitable they were for different ages.
Still, I choose Gcompris any day over apps design around maximizing endorphin rewards and data collection. I just wish there were more quality FOSS games for toddlers.