This is probably the most asked question when dealing with family photos. My suggestions are to choose classic item. Things like jeans or khaki, paired with white or another neutral are a few of my favorites. Don't be too matchy (yes I am aware that is not actually a word but hey, neither is "pinteresty" but I use that too). Although some themed shoots are designed to have matching outfits, and look great, I generally advise having everyone dress similar but not identical. Adding splashes of color for each family member can be visually appealing as well, a red flower in the hair, belt, bracelet etc can be a great way to tie all the outfits together without being overkill. I always tell mom, go find something you feel pretty in and them build the family's outfits around that. Sometimes all it takes is that first outfit to get you inspired for the rest of the family.