I own 2 pet rats, and recently I just adopted a kitten into the same household, although they are in different areas of the house, separated from each other. However even without having seen the kitten, my rats have become frightened and have stopped being playful. I don't know what to do.
I don't exactly want them to 'coexist' I just want my rats to be able to live the same life they did when the kitten wasn't there.
How young is the kitten? How old are the rats? If the kitten is young enough, just slowly introduce them. Use a towel or something with the smell of the kitten and let the rats smell it, do the same with the kitten. If you do that over the course of 3 or 4 days you can put the kitten in a carrier and let the rats smell the kitty while it is in the carrier. You should have no problem, rats are very smart and as long as it is done carefully they should be able to peacefully co-exist.
I had a Chinchilla before I brought in a ferrel kitten. I put the kitten, in a box, next to the Chinchilla cage. They were very curious about each other. Since I let the Chinchilla out to exercise, I needed to have them get use to each other. I was pretty nervous about it at first, but they got use to each other and never have had problems. Everyone teased me about having a dog, cat and "rat". But they acted differently: the cat would chase/play with the dog and the Chinchilla chased the cat!