Yes, a kitten's temperature is taken rectally, but it is best to have your veterinarian teach you the proper technique so that you don't inadvertently insert the thermometer too far or injure the kitten if it struggles.
There is no other way to take a cat's temperature. However, don't try to take the kitten's temperature without the supervision of a vet - you can hurt him or her if you are not careful.
Yes. Rectal measurement is the only certain way of finding out a cat's temperature. Hold the cat firmly while taking its temperature, if necessary ask someone else to hold the kitten.
Kittens don't like to sit still. If you can get your cat to sit while you do this then its okay. But he will be very squimmy. If he's sick take him to a vet.
That is the most effective way of taking a cat's temperature. When you do take a kitten's temperature rectally, make sure you put lubricant on the thermometer so it goes in easier.