Play Aggression

We have a 1.5 year old Male orange tabby that is a indoor cat. He is always going after my daughter that is 9 years old. He chases her bites and scrathes her legs and ancles. He dosen't do this to my other childern, who are 6 and 10, and has never done it to my wife or me. I've been reading some Information on play aggression and think it may be best to get a play mate for him. I just dont know if I should get another male or do I get a female, and do you need to get the second cat around the same age or could we get a kitten about 3 to 4 months old or who this just cause territorial problems? We are also planning on getting a dog in the spring (Lab) who will be in the house often. And if your wounding about my user name, yes the wife got me neutered.

lol. Sounds like you already have a full house to deal with, anyways.

Does your cat tend to seek out the 9 year old for other types of interaction? Is she the one he prefers? It could simply be that he sees her as his playmate if he is bonded closer to her.

Since he does play rougher I suggest a kitten that is older or a cat of similar age. 3-4 months would be small enough that he could push the kitten around a lot. Besides, if you can adopt one already spay or neutered - all the better.
I think boys tend to get along better, but that doesn't mean a female cat would be a bad idea. I honestly find that males tend to be more kicked back and that the older the female cat the more they dislike change. But every cat is different. When picking out a cat try to find one that is friendly with other cats, maybe even dogs, and make sure to read the information in this section about introductions.

Woe woe woe WOE! You already have one animal with a behaviour problem. This doesn't mean you are "bad" pet owners by any means. What he's doing is perfectly naturel for him. He is displaying a domminant behaviour to your child most likely because he feels he can get away with it. However it is some thing unacceptable that needs correcting before anymore pets are introduced! If more pets are introduced it is likely it will only distract from the problem and chances are you could end up with two scratchy biters on your hands! I think you are right in thinking another cat would be beneficial to him. He would have a fellow feline to play with. I think before you do this you need to set the boundries.
First off it is NOT acceptable for him to be biting your 9 year old. Encourage her that when he does this she makes loud sounds that indicate to him that she is in pain. I have no doubt your children love your cat but think about how your child likes to play with him. Does she tease him? For instance waving her hands around his face and when he tries to bite, withdrawing and giggling at him? This will make your cat think chasing and biting is a game. Kindly explain nice playing with the kitty, (in ways that do not encourage biting scratching).
Buy toys for the kitty to play with and chase (these will be a distraction for him).
Also make a rule of if he scratches/bites then he's not allowed to be petted. Arms need to be folded and the cat needs to be ignored because he is doing some thing bad. Your 9 year old might get a bite from him then feel she has done some thing to upset him and then stroke him. This is a big no no, if he has learnt biting and scratching her gets him attention he's just going to keep doing it!
Look at the reasons he doesn't bite you and your partner and the other children. How do you react to him and how does your 9 year old react to him that is different? How do you react to his scratchy/biteyness in comparison to your 9 year old etc.

Good luck ! Hope I have been of some help ^_^