There isn't one "precisely right"
sign for "kitten." In general a good way to sign "kitten" is to sign
"small cat." (Or "cat small.") At the beginning or introduction of the topic you
might also see "baby cat." If someone is signing about their cat and
indicates that it is pregnant and gave birth and then asks you if you want a
"cat" the meaning of the sign "cat" would be "kitten" due to context. If
you have a friend visiting and you lead her to a box of newborn kittens and she
looks into the box and gets a silly grin on her face and signs CAT CAT using a
very small movement and holds the last position just a bit longer than normal it
is obvious that she is expressing the concept of "kitty" even though she never
used the sign "baby" nor "small."