Re: 3 year old being too rough
Each and every time he does it, without any exception he needs to be punished. Talk to him about why it is wrong for him to do those things to his sister, he wouldn't want someone hurting him. Then explain to him that every time he does one of the offending activities he is going to be sent to his room (no playing while there), loss of a privlidge (no tv, loss of favorite toys, no special treats etc), put in the corner (in a quiet spot where he cannot see the tv or he won't be distracted by anything. You can mix up the punishments (i found that out with my son you can't always use the same punishment). You could say, put him in the corner, if he goes in the corner too many times in one day he looses a privlidge, you can also do it the other way, if he behaves for a certin number of days he gets a reward (dollar stores are great for that, you can buy several little toys and let him pick, or you can take him to pick something out).
The key is to punish where needed and to reinforce the good behaviour. Once he figures out the reward/punishment thing he will start to act better, and of course talk to him contantly about it, talk to him about being nice to others, respecting others, why it's not nice to hit etc.
It may take some time depending on how long it takes him to figure out what is going on...but the key is consistancy, you can set up a chart so he can see how he is doing (it could be a discouragement if all he sees is what he is doing wrong, so don't use it if he's having a hard time adjusting), you can use a different sticker for a good day and a bad day....he needs to know that he will be punished each and every time, that is the key, if you let it slide even once out of 10 times he will do it in hopes it'll be that 1 out of 10 times you let him off. He'll probably be punished a lot in the begining, don't feel guilty, after a few days he'll figure out what is going on and hopefully start to improve. Also, if daddy or anybody else is roughousing with him it needs to stop...that teaches him that aggresive behaviour is fun.