We could start by pointing out to school kids how the "one nation" part of the pledge becomes meaningless every time we talk about the "under God" part, which causes all kinds of divisions. Mostly among people who have no idea where the pledge came from or who wrote it. It wasn't Thomas Jefferson or James Madison. The Pledge of Allegiance was composed in 1892 by a Baptist minister and socialist named Francis Bellamy. The original pledge written by him read: "I pledge allegiance to my flag and to the republic for which it stands, one nation, indivisible, with liberty and justice for all." The words "my flag" were changed to "the flag of the United States of America" in the 1920s. Congress added the words "under God" in 1954, when the greatest threat to the United States was the "godless" Soviet Union.
Now as a so-so practicing Catholic, I personally have no problem with the "under God" phrase and am inclined to look at certain litigious atheists as hysterical (I mean honestly, we have bigger First Amendment fish to fry when it comes to our government trying to establish a state religion, *cough* FEMA routing donors to Pat Robertson *cough*). But it is interesting to learn the recent history of something you might have thought "was always that way."