Arranging kids to take a group picture is like trying to herd cats. It's also very entertaining.
First, you have to get them all in one spot.
Second, make sure all accessories are pretty and noticeable, try to keep dresses down, shirts tucked in, and clean any dirty faces.
Third, try to have each child smile at the same time and long enough so you can snap a picture of everyone smiling at once.
Fourth, laugh as each child has their own way of "smiling" and how saying "cheese" means close your eyes.Fifth, be so happy when you get two cute pictures of the kids showing their beautiful smiles and their personalities.