DS2 (9) has got a very red nipple

[Saltire]

and the area around it is very swollen and red, he says its sore, but not itchy. Now to me it looks slightly bruied as well and he did trip and sort of fell over the arm of the sofa the other day,and ended up sort of lying over it, so not sure if it's this or not.

Ok, the bruising has more or less gone and then in the past few hours it has got really red and swollen again and there is a tiny (i.e much much smaller than a pea size) lump where the red bit is!

Don't think I'm going to be able to help much, but fwiw my dd had swollen and red nipple, but no bruising. Turned out to be the school logo on her shirt rubbing on that side (finally out of vests now, see )

This only appeared over the past few days, then seemed to clear up and is now back. The small lump is very hard, and the area around the actual nipple is very red, bright red in fact

Ouch, sounds as if it's slightly infected? I'd get it checked out if it's not looking any better after the weekend.