My 2yo ds was "helping" me chop onions the other day when he rubbed some in his eye. It got very red and angry, and the only thing I could think of doing was putting breastmilk in it. It worked wonders. I hand expressed a few drops into a shot glass and then poured it in. Difficult to express with a 2yo trying to get in there and get latched on!!
Never tried it on nappy rash though. I used to put a little bit of cornflour on it which works on the keeping it dry principle.