"Yee-haw"

When we got back from Texas I noticed that the kids were going around the house saying "yee-haw." I didn't remember hearing that when we were visiting my family. I'm sure that they heard y'all a whole lot, but no one ever says "yee-haw." I finally figured out the other day were they heard it. My friend let us borrow a Thomas the Tank Engine movie for the trip to Texas and one of the characters in the movie says "yee-haw." I was hoping they just made the word up because they miss Texas so bad.