The Challenge

My kids have gotten in a bad habit. Mainly the older two, but I'm sure the younger two will be picking it up soon.
This is what I hear around here.
"aren't I good at such and such a thing?"
"no, you're not"
You get the idea. They do it just to irritate the other one. They could care less if the sibling is telling the truth, they just have to argue it.
Last night I decided enough is enough.
So we issued a challenge.
They cannot say anything bad about the other one until tomorrow night. If they can make it, we will take them out to DQ for some ice cream.
You should hear the compliments flying around here! Maybe it will become a habit. They've said it is much more fun than putting each other down.
One can hope anyway