Hi OP, had to log in to respond to you as we've been living with this for 4 months now with my 6 year old DS and I have found it really upsetting, as well as worrying about spreading to face and hands so I completely sympathise 
I found it so difficult to be told that it could take years to clear up, I haven't accepted it and am fighting it tooth and nail!!
It spreads on cloth and hands, but in particular when a child itches or scratches and gets it under their nails or a blister bursts. So one-time use of towels, pajamas, clothes, never rubbing with a towel in case a blister bursts (just gently dab or air-dry!), keep everyone's nails very short, and lots of hand washing for all of you (your hands and nails can transfer it too). We've been doing this and DS2 hasn't caught it, which is a relief (so far!). Also keep up immune system as much as possible, sunshine (which has been tough this winter), vitamins, orange juice. I don't think it's a coincidence that the spots first came out in the fag-end of winter when he'd had one illness after another, from a heavy cold to D&V and then these buggers popped up.
For the first month I just thought they were skin tags, to which I am prone, but when we realised what it was, on the advice of the GP I ordered a medication off Amazon called Molludab, which is a medication that basically irritates the hell out of the little blisters until they fall off (kind of like burning off a verruca or freezing a keratosis). Some kids don't mind it at all and it works like magic, and I could see that it was working, but after a time my son found it so stingy he would start to moan at me and run away as soon as the bottle came out.
We then switched over to tea tree oil as that is also irritating (but gentler than Molludab). And it seems to be working! We saw the GP today for an update and she said it's crusting over nicely, the tea tree is working the same as Molludab, just more slowly (so unfortunately with more time to spread, which it has down his arm and torso from his original cluster in his armpit). We take a cotton bud and soak it with tea tree oil, and then dab each little blister twice a day. After a week or two the blisters start going very red and irritated, start crusting over and looking dry, and eventually scab over and fall off.
(Unfortunately all this has made his eczema flare up, which is apparently very common with molluscum, and that makes him itch which makes the molluscum spread, etc etc - so we are now doing a full battery of emollients, steroids, no baths, no soap, etc. for the eczema. But that might not be relevant to your DS.)
One thing I thought of was to cover the whole area with a big plaster - that might have helped in the early days when it was just one tiny cluster - but it was so impractical with also putting on the medication that we ended up not bothering and now we are just doing a tonne of washing.
It is utterly shit to feel so helpless - I know how you feel and sympathise wholeheartedly. I'm trying to take comfort in the fact that according to every medico I know, it's a super duper common childhood virus/skin condition, but I see kids on a daily basis and have never seen one covered with molluscum on face and hands right? And neither have any friends who are primary school teachers, swimming coaches, or the coaches at the kids' activities. Which says to me it may be common in armpits and creases of joints but it's very rare to spread to be visible and usually goes away long before it has the time to spread that far. I'm holding onto that idea for dear life.