This is what I am wondering as well. Both of the banks I have used in the past (one large national, one tiny credit union) have special "youth" checking account

This is what I am wondering as well. Both of the banks I have used in the past (one large national, one tiny credit union) have special "youth" checking accounts that can be co-owned by parent and child. Both of these banks had apps that let you transfer money between your own accounts super easily, and like you mentioned, between any accounts at their institutions fairly easily. You mentioned USAA, and I believe they actually let you send money to any old e-mail address (method of transfer depends on recipient and who they bank with). The banks themselves aren't really sitting on the sidelines and waiting for disruption. Lots of them run "incubators" for their internal teams precisely to stay relevant. Apps like this face a real uphill climb.