Bottle feeding kittens?

My cat gave birth to two kittens about a week and a half ago. We noticed the one is thriving but the mother is acting weird toward the runt. His eyes are not open yet and she seems to feed the thriving one more then the runt who is considerably smaller and thinner then his sibling. Should I try botte feeding the runt to see if he improves or give it more time? On a note the mother cat has no objections to me reaching in the cage and petting her or the kittens. Thanks in advance