Style can make a huge difference in the sophistication of your photos. It's a fine line to walk between looking put together and looking like the next Stepford-family; you want everyone to like what they are wearing, but to let all parties go about dressing themselves with no regard to consistency would most likely end in disaster. So how you set parameters that are open enough to allow individual expression without opening the door for Halloween costumes and prom dresses in this year's family photo?
A Better Approach
The best way to please all is to pick a few colors and let those be the only guideline. Traditionally, you might instigate the outfit organization with rules like,
Ok, everyone wear something red with khakis.
We're all going to wear something solid in a shade of blue.
But please, just stop.
Instead, set a palette based off 3 or 4 colors in your home or any other inspiration and let the rest (pattern, texture, accessories, everything!) be open for interpretation!
As long as the pieces stay within that palette, you are pretty much guaranteed to look great as a whole _and_ avoid being all "matchy-matchy." Plus, you'll get a little personality from everyone as they choose pieces they really like and feel good in. Of course, if your toddler doesn't quite grasp colors yet, you might still be in charge of that outfit. But otherwise, don't be afraid to mix and match!
For example, I chose the palette of colors above based on fabric from some curtains. All the outfit samples could be mixed and matched in different combinations and still look picture perfect because they fit into that palette. This also means that you don't necessarily have to go shopping to get the perfect outfits that match. Everyone is sure to have something in his/her closet that can compliment whatever palette you choose!