S.Q.
I would say that it is a trade-off; you just have to weigh the pros and cons. I do believe kids will get sicker spending time in such places. Even if the toys are cleaned regularly- which I suspect they are not- the kids are probably all over one another, acting like kids: fingers in noses, mouths, drool, goo, etc.
I work one-on-one with kids and I disinfect each set of toys and surfaces between each child. I use sheets to cover mats when babies crawl. We wash hands when we enter and leave the treatment room. And kids probably still get sick in my care!!
You are giving them a chance to build their immune systems while they are socializing and you get some mama-time, so those are sure pros!
I'd just keep an eye out for anything unusual and encourage your kids to hand-wash (or bring your own wipes) and wash their hands when they enter and leave the playroom.