I'm going to beat you up!

My kids have been really competitive lately. The phrase I hear a lot is "I'm going to beat you up!" It means, we are in a race and I am going to win the race.
I think it stems from our race "up" the stairs and me telling them that I was going to beat them up. I guess I needed to clarify that I was going to beat them up the stairs and not that I would knock their teeth out if I won.
I've tried to correct the misconception that they have, but it is no use. I try to have them phrase it as winning, or being faster, but they insist on the phrase that sounds violent.
Last week they drew attention to themselves as they raced up and down a ramp at the mall shrieking that they were going to beat each other up.