Any 10-year-old should be able to change a light switch!
However the RNIB website suggests simply using a suitable coloured tape to outline the switch:
"Use switches and sockets which contrast with the walls. For example, a dark red light switch would contrast well with a white wall.
To add even more contrast, you could put a contrasting light or dark strip of tape around the outside of the switch"
http://www.rnib.org.u...ical_adaptations.aspx
If it's a light-coloured wall, a square of either black or brightly-coloured insulating tape around the switch would probably be just as good as anything more expensive. (Obviously, if it's a dark wall, white tape would be better).
Chris