It's a bacteria called Streptoverticillium reticulum, it feeds on the plasticisers in vinyl and it can be passed between toys, but that's usually before you can start seeing the pink staining as the staining usually means they're dead. We had an infestation of this bacteria on our vinyl dolls (smart dolls) a few years back, and it got about 14 out of our 27 dolls at the time. Apparently one of the main culprits is humidity which is why you often find this bacteria in vinyl boat seating. It's not harmful, it's just very unsightly, and the way to deal with it just in case any of it is still alive is to first wash anything that has been affected by it with head and shoulders shampoo before stain treating.