Take the above suggestion as soon as possible, they may have a cold. This can be very dangerous for them. Make sure they dont have dry discharge in their noses, if they do, this needs immediate attention because they will not be able to smell with plugged noses and a cat will NOT eat what they cant smell.
If they are just born they may still be getting fluid from the womb out of their lungs but this shouldn't be needed for long after the birth, so still take them to the vet.