Patty-
Great Commission! Congratulations again!
Yes, I would shoot in one day. Chris has a great suggestion (hiya Chris) about scoping out the location beforehand for lighting, best place, etc. Here's what I do with groups and otherwise:
Bring your laptop on the day of the shoot to download pics in stages
privately. Keep the kids away. You decide the best poses. Reshoot what you have to. Show the kids their positions, and get those individual shots. Sometimes they aggravate each other in group poses which brings on more tension. Download those to make sure you have what you need. Repeat all the above in a different location, and different lighting if you have time. Once YOU finalize the exact composition of ALL of them, show the parents.
Do not allow the parents to be there. My humble opinion. Of course, I have a great evil eye
