I’m absolutely certain you could train them on that.

I stood outside the art place at the beach for three or four hours one day when I was bored helping people see them.

I believe anybody with reasonably corrected binocular vision can be taught to see them.

Almost everybody that can’t do it is trying entirely too hard. They’re looking for details in the wash instead of letting their eyes uncross and relax. You simply need to use your distance eye crossing while using your reading vision focal points.