In our last home we added this feature when we remodeled our basement. My husband simply cut into the sheet rock and added an entrance that our cat could fit through. This way the kitty food, water, AND litterbox are not accessible to the kiddos and we can leave the laundry room door shut, but the cats still have access. Genius I tell you, genius.
When we moved, we had the food and water and litterbox in our upstairs half bath that is rarely used. It was a pain trying to keep the cats fed and the little ones out. It lasted while we finished the basement and I'm glad it's now done.
This is our new kitty door. It goes into our water heater closet where the cat necessities are. Away from our one year old, as well as our dog. It's clean, out of sight, and the animals have their own little peace and quiet. Plus I think it's genius.