A hard and fast rule for clean up and work projects

Don't let adults clean up in place of the youth. This is bad for everyone involved but a natural tendency. The adults resent it and the youth get used to being waited on. Make it a policy that no adult works until all the youth are working. If a youth spills, they clean it up themselves.

Now this needs to be done in a non-confrontational, hostile or us versus them attitude. It is not: “We're the adults and you are the youths, not get to work.” Rather, “This room belongs to you and I know you don't want it trashed or run down, so you'll need to get hopping on cleaning it up – I'll get the cleaning supplies for you” or some such positive but firm approach. 

At first you may have to gently wait them out. They may not believe you are serious and will eventually intervene. When an Adult starts to jump in, gently take the broom from their hand and hand it to a youth. And so forth.