How can i get my kitten to eat her own food cat to eat her own food?

I just recently adopted a kitten and I already have a cat. And after the hissy fits subsided, they started eating the others food. The kitten eats the cat food, the cat eats the kitten food. I put the food bowls in separate rooms... But they just go to the other bowl and eat out of that one. What do I do? How bad is it for a kitten to eat cat food? Or a cat to eat kitten food?