Sometimes it's just personality, but I have found that most kittens do grow up and mature, and grow out of the kitten "crazies." Your boy might be looking to re-create the rough and tumble play he engaged in with his littermates. Is he just playing rough, or actually fighting with them? If there is no hissing, growling, spitting, then I would say it's normal, he's just more rambunctious than your older two were as kittens. If he gets out of hand, your two will surely let him know with a well placed swat.

It sounds like normal crazy kitten behavior to me. :) They will push the limits learning how to attack and stalk around that age. It is adorable to watch them practice, but not always so much fun for the one receiving the full attack.

Personality is defiantly part of it. Our current kitty took a full year to mellow in the slightest. There were many sleepless nights with him tearing around the house, diving and attacking everything. Neutering did help, but time was the major factor.

If the resident cats were older or in poor health, I'd be concerned if the kitten was bullying them; but in most cases cats work things out among themselves. Even passive cats will find away to balance things out and teach the kitten how he should interact with them. Sometimes it is by their refusal to play/interact with them when they are too rough.

If they are a little over-whelmed right now from the change, I'd recommend giving them refuge from the little guy and some one-on-one time daily. Perhaps confine him to one room during the day while you are at work (giving them their routine back) and only let him out with the others in the evening.

It's only been a few weeks. Cat's are not fans of change. ;) Give them a little time.

Sometimes it's chemistry. And some older cats do not enjoy kittens.

Thanks for the input. I greatly appreciate hearing about others' experiences. The kitty is just playing -- doesn't hiss , growl, or spit. The older female has hissed at him to make him back off, which I consider the "mommy-kitty" response which is good. It's the older male who has been totally intimidated.

It is probably the kitten crazies and it is play that he probably enjoyed with his siblings. They could jump around on each other and bite and wrestle. My older kitties aren't into that behavior!!

The older kitties are in good health so I hope they can figure out how to handle the new guy. I do give them time alone-- I work at home so during the day they have more time together. In the evening, the baby retires to his part of the house so the older kitties have quiet time with me.
Thanks again for the input. I will try to be patient. This is probably harder on me than on them!!

He is only 12 weeks old! Of course he is going to want to play.
In my opinion,you are lucky.When I attempted to get a kitten my cat was so angry he not only hissed and growled at the kitten,he hissed and growled at us and started swatting at us too.You couldnt go near him without him looking like the evil cat from Pet sematary.Frankly,he made me so mad I wanted to keep the kitten and send him packing (but I didnt)

My advice,if the kitten gets too crazy,just put hijm in a room by himself for a little bit.Or,clap your hands loud when he starts bothering your other cats and say,"NO!"
He will get the hint sooner or later.Or,get a squirt bottle and take aim when the kitten starts attacking them.

It's good there's no hissing/growling or seriously nasty behaviour from the kitten. Give it a bit of time, and they'll work it out among themselves. Yes, give him a time-out if he acts too crazy; I sometimes throw a small cushion just to distract the resident hooligan Jas-purr when he gets Coco's neck in his jaws n she screams as if she's dying LOL

Two of our older cats are OK with the kittens; Nikita (who wud dive under the duvet whenever she saw a new kitten around) now mostly ignores them/hisses at them/sometimes bathes them; Max (17lb) plays with them, then sits on them, but they're 6 months old now and can get away from him, and we know he means no harm.

Now Simba **sigh** - I hate to see him looking for new places to hide from the terrors - he growls, hisses, swats at them all the time. And now that they're all grown up, these two don't think twice about jumping on his back as he passes under the chair on which they lie in wait. If they bother him too much, I give them a time-out for 10 mins. But these days they're getting to know the routine so well that the minute I clap and say OK guys, time-out! they actually run to their room, heads held high and tails swishing - probably thinking oh yeah, the mad witch just has to spoil the fun LOL

Plasticgarden, how did you help your cat get used to the kitten eventually? Simba doesn't hiss/growl/swat at us, only at the lil ones, and I don't like it that he can't be at peace with these guys around. Feliway worked for a while, but didn't calm him down enough to stop hissing and growling.

Pranjal,it just takes time.I read somewhere it can take up to a YEAR for cats to develop a friendship,and some may never become friends,only tolerate each other.