A very common question that I get asked from families is "What should we wear to our session?" Of course you want to look super awesome and have everyone coordinated. You don't need to, nor really should everyone be exactly the same. That would just be too boring. :)
I like to tell people to choose a color or two and build off of that. For example...little Suzie is going to wear a super adorable little dress that has pink flowers with green and blue accents. Now we just build from that. Mom can wear blue jeans with maybe a pretty green sweater. Dad could also wear blue jeans with a blue polo...if you wanted another layer, than Mom could add a scarf in a subtle pink print. See where we are going with this...layers, texture and coordination, but not all the same.
Pinterest has, of course, a wealth of examples. Just type in "what to wear family photos" and start pinning!
Here is a really good example of a family that nailed it when they came for their family session this summer. I just happen to have a backdrop that was perfect!