You will be moving, sitting and standing in these photos. If clothing is tight or uncomfortable, it will show. Please remember the connection you share as a family is what's important, not your outfit!
Rather than matching outfits, focus on color coordination. Choose a color theme if possible (for example navy/grey/cream) and work around that. Also decide whether you are going for a more casual or dressy look and weave that through your outfits.
Complement but don't match
Spring? Softer pastel colors may be a good choice. Summer? Think white, yellow, bold red, orange, pink, turquoise, royal blue. Browns, mustard yellows, burnt orange, dark greens and purples are great for fall. Creams, brown, black, gray, ruby red, dark purple, emerald green or blue are good for winter shoots.