For the case of blind, elderly and children, they can still be able to cope up on using digital payment methods by having reloadable card like we can use on train stations for easily accessible way of doing payment by simply tapping it into the system. If that would be the case on how they can use their Bitcoin by loading it into a card like fiat getting into digital wallet going to a card for loading, that would make an ease for the hardship they are encountering on using digital payments such as Bitcoin payment if ever available. But for those who can freely access and know how to properly use their Bitcoins, that won't be a problem anymore I guess. It is just in need to put up a solution to the problem to be able to deal on the fast pace of modernization.
What about systems like Siri where you can give commands via speech? Wouldn't that be the simplest way to interact with your device in order to get transactions initiated and processed? For verification you could use fingerprint in addition to a spoken password, just in case someone listens to you. The password could be a certain sentence as well so it is not that obvious. I think there are ways for sure to solve such problems.