Oh your poor DS
DH is an eye surgeon - he says irrigate, irrigate, irrigate - get a bottle of water and pour it on. Could also try cleaning the lower lid with a cotton bud if you're brave. Basically he will keep rubbing for a while but if he doesn't settle tonight or is still rubbing in the morning you'll have to head off to A&E I'm afraid. Moorfields if you're in London. HTH.