I'm having a high school graduation party?

and I want it to be fun for everyone. There will be families there, adult friends of my parents, and my friends. I was thinking it could be turned into an alcohol party later on? do you think this is unadvisable...I was also thinking it would be nice to just have a barbeque..any ideas?
Update: i live on the lake so that's available..and we'd have alcohol for the adults so i guess that would be great...any more ideas for things to do to keep it lively? thanks guys!
Update 2: woops i meant we'd have alcohol for the adults not the kids...drinking would make it all a lot more complicated...plus my some of my friends and i dont drink all that often..we like the sober life
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