I prayed for inspiration, and grit my teeth as I headed down to our supply closet to look for costume or prop ideas, that would not require explaining as the children's involvement is almost completely improvised (except for a few whispered instructions as the groups wander in).
I ended up making some funny improvised "costumes" for Noah, his wife and 3 sons, which I ended up pretty excited about. They were basic enough to throw together quickly, yet very fun for the kids to wear (maybe because they were so ridiculously simple). With the current trend of beards and mustaches going around, I knew that any facial hair prop was sure to be a hit (even for the girls).
I found funny beard templates from the family fun website, which I traced onto different colors of construction paper (you can find the same templates here). I ended up having to use some masking tape pieces to hold the side burns in place as well as yarn to tie the beards onto kid's heads.
When I was digging through a box of yarn looking for something to tie the beards on, I found some delightful fat yellow yarn that looked to me like tight blonde curls. I decided to also improvise a wig so as not to leave Noah's wife out of the costuming fun. The yarn was already cut, so I laid the pieces out on some masking tape to make a perfectly silly wig.
I ended up really having a lot of fun including the kids in the story. The kid volunteers did an awesome job acting out even the parts I had not given them any instructions on. Of course, there was the element of chaos, as would be expected. Even the chaos, however occurred at the right and expected moment, during the flood when Noah and his family got to squirt the audience with spray bottles. Let's just say, the "flood" didn't want to stop, and could have very well last for 40 days and 40 nights without a little intervention. Also, only one of the beards survived said flood for me to take a picture of it the next day. :-)