According to these links catnip is not okay for kittens and some cats. The catnip could give the kittens or some cats chemical imbalencement in the brain and have the cats act out in wild and erratic behavior.

“That allergic reaction makes some cats and a lot of kittens especially literally crazy and not in a good way.”

I give my kittend and cat catnip. Not all the time but now and then i will sprinkle some on the thier scratching post or on their little beds. Usually when they get into the cat nip they end up hyper and crashing later. They do not show signs of attacking randomly at any humans but they do going a little wild on one another. Iv always thought catnip was okay for every cat. Then again I never checked the catnip product for any warning labels. Now that I know to watch for my cats behavior on catnip I will look for signs to make sure they arent having a chemical reaction. I wouldnt want it to have a long term affect on my cats.