Well, the cat is happiest inside, but should you need to keep them outside, it's desperately important to keep their shots up to date, their flea treatments on them, and they have to have a warm, dry place to sleep and plenty of fresh food and water. And of course, LOTS of attention and love.

If you can't keep them inside exclusively, then at least consider letting them be indoor/outdoor. They can come in, eat and relax and have cuddle time with you.