ds1 had molluscum for six bloody years so am a bit of an expert 
it's a pox virus, same family as smallpox and chickenpox, causes little pearly white warty lumps which are highly contagious as it can live on almost any surface for quite a long time and also travels in water.
most kids who get it will only get a couple of them and they usually take 6-18 months to rid themselves of the virus completely.
it seems to be something some people are more susceptible to than others though. i caught them from ds1 and had them for couple of years on my neck, very attractive. but ds2 and dd and dh have never caught them despite sharing obviously close contact with him.
the most effective thing we found was a herbal tincture i ordered from America (not terribly expensive though) called Virucide/Zymaderm.
there is also a cream you can buy OTC here called crystacide which has very good results for i think about 80% of sufferers. it's v expensive so not available on NHS. also IIRC it's not licensed for use on molluscum, but it was ds1's long suffering dermatologist who rec'd it, so is definitely safe!
if there's only a couple of them, they can be frozen off - ds1 had them all over his entire body so it wasn't feasible to do though we did try a couple at one point.