Actually, you could let the supervisor to immediately restart its children and implement what is called lazy initialization:

1. The supervisor (re)starts (immediately) the child (say, a gen_server)
2. The gen_server returns a 0 timeout in its init function
3. In the handle_info you do an active wait (your 10 seconds) to ensure the DB is properly initialized
   This way, you ensure that all requests to the gen_server are processed after the DB is properly initialized.