Not all 12 year olds are in a single social group. If one is being left out because they don't have an instagram account, there's another social group they can gravitate to that has other interests besides instagram posts.
no, there isn't
In many ways hanging out with kids who are banned from social media is hanging out with kids from a pretty exclusive club. This is why unless you homeschool it is REALLY worth it to put your kids into school where parents are from a similar group as you are.