Clothing is really a personal choice but with a little planning it can really enhance your photos. Clothing with logos and graphics tends to be very distracting so it is best to avoid these. There is no need for everyone to match but but it is a good idea to have everyone in colours that coordinate with each other. Layering is also great, especially on cool days! Additional tips can be found here: http://clickitupanotch.com/2013/10/what-to-wear-in-family-photos-5/
Newborns are best photographed wrapped in a blanket or scarf. Outfits typically overwhelm their little bodies and tend to just make them uncomfortable. Personal touches can be added with hats, headbands, special pieces of jewelry or family heirlooms.
All sessions can incorporate items special to the child, couple or family. An old wagon, a favorite book, a family rocking chair or a beloved stuffed bunny are just a few examples.