Often one of the questions I am asked when a session is scheduled is; "what should s/he wear?" It's a great question, and shows that your child's portraits are important to you!
I love color, and coordinated pattern! Pattern as an accessory adds just that bit of spunk and personality to portraits. This time of year especially your child's outerwear is very important too.
When selecting clothing for multiple children, pick one or two colors that span all outfits, then add another color (or two) to each outfit. For example, 2 children - a boy and a girl. You could choose brown and white plus denim as the base for both outfits. Then add some blue, green, or red to the boy's outfit and add pink, turquoise, or purple to the girl's. Voila - your children's clothing coordinates but doesn't match!
You don't need to go out and purchase new clothing for your child's session, but here are a few ideas I've put together that you could use for inspiration from your child's own closet:

