I have no idea where the phrase originated. My own kids said it when they were young. But I did not teach it to them.
Today I learned that my first graders are saying it.
As in, "I am versing you in a game of Connect Four." Or, "Did you just vers Christy?"
Our computer lab teacher heard them today and told me about it.
Perhaps tomorrow a lesson on the phrase (and variations of it) "I am playing against you."
Or does it really matter?