This is just me and some of my paranoia. I hated Vegas and wouldn't even consider taking kids there. My one and only panic attack happened in Vegas. I felt sick most of the time because there was no where to escape the cigarette smoke. Even outside it seemed like one big ashtray. I was uncomfortable with a lot of the advertising for burlesque shows, escort services, strip clubs, etc. I don't consider myself a prude, but I definitely would not want my 6 and 8 year old seeing some of the those things. There are lots of areas of Vegas (on the strip) where kids under 18 can't even come in. I don't remember seeing many kids at all when we were there. Vegas just seems like an adult vacation to me.
I would not be comfortable with leaving my kids with total strangers, even if they are highly recommended. I have a hard enough time leaving my kids with my SIL who I know very well. And knowing my kids, they would be very uncomfortable being left with a complete stranger, even in a "kids' club" type of setting.
I know people take kids to Vegas (and a good friend of mine grew up there), but personally I'd rather take my kids someplace more kid friendly if we are taking a family vacation.