I follow a 5 basic steps when I style my kids for our family photo shoot every year to avoid that "matchy-matchy white button down, jeans with barefeet" trap.....
For our 2011 shoot, I found a really cheap pair of red headphones that I knew The Dude would love wearing and that inspired an urban theme...like the kids are waiting for the train into the city. I always mix accessories I purchase for the shoot with staples my kids already have so I don't break the bank. The goal is always to get the kids to coordinate, not match! Have fun with it and use your imagination when it comes to the clothes, theme and location.
My best advice is by mixing in fun pieces you can create a ton of interest in your photos and highlight everyone's individual personalities. Avy loves all things glitter and fancy but she still loves being a little tough. The Dude just loves to be the hippest guy in the room, he's obsessed with clothes but is also a total ham...and I think these pictures really convey that. If you're kids love the outdoors or nature or baking, use those as jumping off points when thinking about your theme and location.
Another important element is a bad ass photographer, my friend Meredith of Meredith Mascola Photography took all the photos in this post and does our portraits every year. She is great at getting the best out of my kids and that's key, they are always laughing and smiling with her. Plus she gets my crazy visions every year and really helps me achieve what I see in my head. So shop around and if you like the style of someone's photos ask them who shot it and give them a call.
And when you get those pics taken, send them over to me and I'll help you create a unique holiday card to really wow your friends and family! !