i used to give my cat 1 baby aspirin every other day for arthritis pain (as recommended by his vet) THERE ARE SIGNIFICANT DIFFERENCES HOWEVER - my cat was about 3 YEARS OLD when i did this and it was for CHRONIC PAIN. Now he takes cosequin for the arthritis. I WOULD NOT medicate a kitten without being examined by a vet. There are lots of questions raised when a kitten is hurt. Can you provide more information? Maybe someone can give you better advice.
Don't give a kitten aspirin without checking with a vet. Aspirin is used to regulate temperature, and kitty's temperature will vary over a two hour period by a few degrees normally. They also don't process it quite as well as we do, so unless instructed, it's not a good idea to do.
Unless a cat's temperature spikes above 102.5 (high normal) to about 105-106, aspirin is best avoided.