Deciding what to wear for a family portrait session can be quite a daunting task. But it doesn't have to be! Here are a few tips that can help you coordinate your outfits. 1 - Decide on a Color Palette / Choose A Focus Item The very first thing you need to do is decide on a color scheme. This is probably the hardest part...but no worries - there is inspiration all around you! For a starting point you can do one of two things. Find a color palette you like or choose a focus piece. From there you can move on to the other.
If you want to start with a color palette, one of my favorite websites to look for inspiration is Design Seeds. This website takes a close look at the world through images and pulls out the coordinating colors which are pleasing to our eye.
The great thing about this site is you can choose colors based on a theme. Some of the themes are seasonally based - perfect for planning out your wardrobe!
I encourage you to visit this site, although I'll warn you it's easy to get lost enjoying all the beautiful imagery. Oh, and do yourself a favor and bookmark that site, because it sure comes in handy when it comes to home decorating!
If your find this a bit overwhelming, you may want to start by choosing a wardrobe piece that you love. This may be a plaid shirt for your son, or a cute floral dress for your daughter. Once you find it, you can pull other colors from that item or plug a color from that item into Design Seeds and find more coordinating colors.
Coordinate Coordinate - don't match. Yes, these are two different things! You want your family's clothing to compliment each other - not be the same, or variations of the same. Continually refer to your color palette and choose complimentary colors.
Accessorize & Layer Up
Accessories add interest to any photo. Grab a scarf, a necklace, add a tie or hat. Add a headband or bow. Think outside the box. The best thing about accessories is that they are easy to add and remove and can change the look and feel of the image without having to do a full clothing change. Sometimes the simplest accessory can make the boldest statement! 
Evaluate Once you have everything picked out, clear off your bed and lay everything out. Take a moment to look at all the pieces together to make sure you are happy with the choices. Swap out anything that stands out or doesn't coordinate well.
Keep it Classic & Comfortable
Choose clothing that is timeless! You don't want to wear something that is going to look dated 5-10 years from now (think back to that 80s neon trend). Simple dresses, jeans, neutral shirts all work well. Perhaps the most important thing to keep in mind for your children is that the clothing should be comfortable. The last thing you want is to have your child spend the entire photo shoot tugging, pulling at their clothing complaining that it's itchy! 
And if you need a little more inspiration, check out my wardrobe boards on Pinterest for ideas!