I get paid for gigs every week and don't have that kind of gear. lol You should be fine. I agree with many of the others, the 5Diii and 24-70ii should handle the entire situation just fine. If it's an outdoor gig, I might go with the 70-200ii, but even then I would probably rely on the 24-70ii. I don't like flash, I use it when I have to. I almost always have it on (just in case), but rarely will I use it voluntarily if the ambient light is there.
Stay calm, chat with the kiddos, be professional, and you'll do great!