I like your idea of creating a blockchain social media that can hold the same potential for younger students as it does for older ones. In early childhood classroom that support socio-constructive learning and reflective practice, it seems that having some kind of constructive social media forum could support the child’s learning in some really interesting ways. It seems to me that one of the challenges lies in creating or providing something that is developmentally appropriate, in addition to leveraging the use of tokenization and relying on data security via the blockchain. But perhaps that could be remedied by establishing a clear set of guidelines or norms up-front.
As far as how this might be designed or implemented, I think the ideas you have shared here are sound. As you point out, even if they were not able to read or write yet, young learners could still share their thoughts via audio or video recordings. And adapting the social media platform through gamification or visual learning adjustments makes good sense. In any case, this would make an interesting teacher research project, the results of which could then be used to drive a new product innovation. Who knows... maybe IDEO would be interested?