Why Is My Nursing Cat So Thin Even Though She Has Been Eating Kitten Food Whenever She Wants?

my nursing kitty is very skinny and i know she has been eating kitten food. always eats alot of it but no more than a few times a day and some days just one meal, what can i do to help her gain weight?

why does my cat eat only after midnight even though he gets fed at 7? how can I encourage him to eat earlier in the day?