Don Liu <ddliu0@yahoo.com> quoth:

They're probably just doing a combination of playing and honing the skills
they would need were they to be living wild.  This is very natural for
kittens and should not be discouraged.  One thing they're learning is what
hurts.  They don't really know that until they do something and then the
other one complains.  Then it registers in their little furry brains as
something that shouldn't be used for play.  You *want* them to learn that!  
It's sort of like human kids learning empathy.

Here is a pattern you will probably see as they learn:  A will do
something to B, and B will either whimper, screech, or hiss briefly.  A
will immediately stop.  After a moment or two play will resume.  This scenario
is the learning process in action.  A has now learned that what they did
causes pain and should be reserved for only necessary occasions.

Here's a pattern which means they've moved beyond play/learning and are
genuinely fighting:  A does something to B and B whimpers, screeches, or
hisses.  A does NOT stop, and B continues to cry about it.  That is what
you want to break up.  You may not need to physically separate them, or
maybe only until they learn that That Tone of Voice from you means "cut it
out now, buddy boy!"

In summary, most rough and tumble between two kittens is normal and to be
encouraged.  When one complains vocally and the other doesn't respond
appropriately (doesn't stop), that's fighting.

Relax.  They're probably just playing.  Have fun watching their antics!

Priscilla

 

are you sure they are not playing?  that's how kittens play, they
play-fight.  also, if you give them attention when they play, they
tend to paly more.  as long as neither of them screams like they are
in pain all the time, they are fine.

-L