Cats eating

Question
just a quick simple question  I have 2 cats one everyone says she is the runt of the litter.. She is super slender and just over all a very tiny frame just barely 6 lbs  she is just under a year old.. All up to date on shots and fixed the vet has never shown any concern.. Her sister was always a very strong athletic build she has become very stocky.  Just 9-10lbs
  They both eat the funny part is I always see the thin one more then any of them.  Theres always food in there bowl we feed them 2 times a day.  But they eat all day not all at that sitting..  How can I fatten up the other one and keep the bigger one under control as I do not want her to get any bigger.
Any ideas

Answer
Geoff,

At under a year old they are not through growing. Also cats are like people, some have small frames and some are husky. The cats may be sisters, but they could have different fathers which would explain why they are not the same build. A female can have a kitten by each tomcat that bred her during her cycle.

As long as they are healthy and playful, I wouldn't worry.

Tabbi