"Focus on coordinating and complementing each other - not matching" is the best advice I can give you. When your significant other or children want to join in the session, coordinate but try not to match. Matching 100% is often overdone and not very flattering. It looks so much better when you coordinate with a similar color scheme for everyone in the photos. Maybe neutral colors for the guys and pastels for the girls.... Something similar but not exact! If you need more help with colors, I’ve found this easy-to-use online tool: Color Scheme Designer: http://colorschemedesigner.com/
As a mother of three myself, I understand that after having a new baby, you’re not always feeling your best. The most important thing is that you should feel comfortable in what you are wearing. For Mum, warm soft neutral tones in greys, beiges and pastel tones are ideal. Remember that the images will be closely cropped, and your baby will be the center of attention in the image. Your hands will however be visible, so it is important to have either nicely painted nails in a nude colour or no nail polish at all, with nice clean nails. Feel Beautiful - I want you to do anything you need to do in order to feel beautiful on the day of your newborn session. If that means hiring a makeup artist or getting a blowout, then do that. If it means splurging on a brand-new dress that makes you feel exquisite than do that. Trust me when I say this, how you feel about yourself will make a big difference in how you see the final images from your gallery.
I recommend plain T-shirts, whites, greys or beiges are great, but also please bring a simple black T-shirt with you. A white button up shirt is another option if you’d prefer that. Very often I photograph Dad's with no tops on, of course it's up to each of you if you want the on-skin shots or to show off tattoos. A haircut and beard trim or shave will make Dad look and feel good. Clean hands and nails are most important, especially when photographing your tiny newborn baby in Dad‘s hands.
Pretty much the same rules apply for Mum & Dad. Bring some lightly toned outfits. I would avoid wearing fluffy dresses and tutus, as it takes too much attention away from your newborn. When a sibling is holding baby, I tend to leave baby wrapped for safety reasons, especially if the sibling is in the 2-4yr range (toddlers are wiggly and can just let go!) I have heaps of gorgeous wraps to suit every wardrobe, so you need not worry about that at all.
No Logo's or Checks
No thin stripes, they cause a weird wavy blurry patter in your images.
No neon colours
And no shiny fabrics.
One more thing, Shoes & Pants – don’t worry about your shoes at all, your feet will not be in the picture so make sure to wear some comfortable socks lol! Pants could be in the picture just a little bit so dads can wear jeans or khakis and mums can wear whatever is comfortable (black or white yoga pants are perfect!).