Get off of there!

Why is that animals are attracted to sleeping the things you least want them on. Our cats will not stay out of my children's beds which for some reason drives me crazy. I am considering purchasing some cat furniture to see if I can't entice them to sleep elsewhere. My older son has allergies that are fairly well controlled but I don't like the idea of our cats sleeping on his pillow if I can stop them. It seems like every time I turn around one of them has found a way into his room and is curled up smack dab in the center of his pillow. I am fairly sure my toddler has learn to say "Get" simply because he hears me yelling it at our crazy cats throughout the day.