Fair warning disclaimer: I don't have kids, but do work with them. Your mileage as a parent may vary.
It really depends on your kids and what your tolerance is for things. I don't think you'll see any really lewd or exceptionally rowdy behavior, but after people get some drinks in them, that could change.
You can definitely expect to see people walking around with drinks, people smoking, and people who are intoxicated. You may see some mildly skimpy club attire such as short skirts on women. You may very well overhear some foul language from other patrons, since people are drinking.
I would also possibly suggest not doing the Adventurer's Club if you don't want the kids listening to mild double entendres. While nothing there is obscene, some of the jokes are mildly adult- I don't think they'd hear anything terribly scandalous, but some of the humor will go right over their heads, and some of the skits definitely mention drinking alcohol. That may not fly well with your DARE-aware son.
I think if you go earlier in the evening before the partying is really heavily underway, you probably don't have too much to worry about. I might be a bit hesitant to have pre-teens there later at night when some people may have had a few too many. I've never witnessed anything worse than a drunken verbal argument in the street, which was broken up pretty quickly, but you may want to make the choice to not expose the kids to drunk adults whose behavior may be unpredictable.
