13 year old cat will not use the litter box!?

Cats normally start peeing/pooping outside their box when they are stressed out. My cat started peeing on the floor when I had my daughter. It freaked her out. My mom recently started having the same problem since my now toddler goes over there. Little kids/toddlers cause cats alot of stress. There is this new product called Comfort Zone which helps relax cats - which ultimately keeps them from going outside the box. Its supposed to be a great product that really works. I haven't tried it yet, but I'm gonna buy it. The only problem is its kind of expensive. $50 for the plug in & $20 for refills. But you can get coupon from website. I listed it below.