Cat Aggression - Please help!!

[Elmo0713]

I have a 10 year old tabby who acts aggressively at times towards my 5 year old. This has not always been the case (but he is definitely better as an only cat in the household - which he is now).

He is cuddly and sweet with me especially. My daughter is so careful around him (she knows not to go close to him or pet him unless I am right there).

An example of things that occur:
1. She will just be standing in the room, he will wander over to her and then just swat at her leg - she does not provoke him at all)
2. He will sit in the middle of the room (even though he has lots of perches/cat tree/beds) and if she walks past him he will swat out at her and sometimes even bite.

I have tried playing with him to tire him out but an incident can occur right after I do this. It seems random and we just don't know what to do. My daughter has learned to be scared of him because she never knows what he will do. He does not do this with myself or my husband and it does not seem to matter if she is running around (actively playing) or just standing quietly.

Please any help would be so appreciated. I love this cat so much and want to find a solution.