所以就用runner to change its color as decoration; it also prevent anti-slippery effect. Again, with kids, we just have to do something "sepcially" out of our mutual convenience, which is not always the best!
I bought double-side tape to fastern the runner, I used screws aswell.
It will be hard to fix runner on top of carpet; you probably will have to change it completely if you don't like your current color. Safety is always the most important, having runner on top of carpet is not safe, I think.