I have done this with a puppy but not a cat. Once I realized that the pup was not breathing I began to massage its chest ( squeezing just hard enough to feel the ribcage compress a bit to get the heart pumping ) and using your mouth to cover its entire muzzle ( nose and mouth ) blow an ever so light breath into its lungs after every 5 or so compressions of the chest. It may not be the correct way but the puppy lived.
Average weight of a newborn kitten is about 3 ounces.
You will know when a newborn kitten is dead when the kitten is no longer breathing. The kitten will need to be taken away from the mother and disposed of.
From a cat
How do u keep your dying kitten comfortable
Go to google and look up newborn kitten pics and it should have some.
take it to the vet
In Hollywood you can.
to stay cool