We did something along Rabbit's suggestion and the photos turned out great. We kept things fairly simple. Dark greys, a bit of cream, dark plum, and a muted magenta. What stood out to me was how well all the textures worked for us. So not planned. But we had corduroy, lace, ribbed tights, and heavy cotton flannel. Our photos were done in October in a wooded canyon and the fabrics just seemed at home. I also liked that DH and I had on outfits that played as a background to the kids. I wore a slightly fitted thin knit tunic sweater in super dark plum with dark jeans and boots. I could move around and not worry about how my clothes looked. DH had on a dark grey shirt with the faintest check/stripe and dark jeans. The muted magenta - brighter plum than my sweater my oldest wore with a dark grey skirt and tights. My youngest had on a cream top with lace, a grey cord jumper, and stripped tights.
Our photographer suggested having something for the kids (3.5 & 1.5 yo girls) to do - balloons, pinwheels, bubbles, etc. since kids are not always into having pictures taken. We borrowed a wagon from a friend which worked out great except, it was bright red. Not really in our color scheme. We got some great shots using the wagon but ended turning most to B/W.