How can you kill fleas o 2 weeks old kitten?

Vinegar will not kill fleas on any animal.

Bathing is the best option. The safest flea product on the market for kittens is Revolution which you can use in kittens as young as 4 weeks. However, you can use Advantage on a nursing mother which will protect the kittens as well.

The best thing i have found for killing fleas on a kitten is dawn dishdetergent. wet the kitten cover it in dawn scrub it good and leave the dawn on for 10 min. I know the cat will not be happy but it will kill the fleas and wont harm the kitten like some chemical ones can