We just finished a 4 day visit to Disney World.  there were 8 adults and 7 kids.  In order to keep track of everyone my wife bought royal blue baseball caps for everyone.  We all wore them every day and we were always able to find the members of our party whenever we were separated.  The bright blue color was very easy to see at a distance and was very distinctive.  It worked really well.

Another advantage of all of us having the hats presented itself when cast members started referring to us as the “blue hat bunch.”  This recognition helped us several times to get the entire group on rides in adjacent cars or boats instead of being separated.