P., I am going through te EXACT same thing right now. My 2 yr. old is doing the same thing to my 1 yr. old. She has been hitting him when he is trying to play with a toy or pushing him down by his face when she gets mad about what he is doing , even if she wa not interested in the first place. It can be very frustrating. It has just started happening more and more recently. I have found that sometimes when I catch it in mid stream I can redirect her to something else that she has or can do so she stops but when I have to pt her in time out I usually take he to another room and make her sit, wether it is on the steps or on the floor but away from the situation. I tell her she has to sit and if she gets up I just take her back to where she was and make her sit again. until she is allowed to get up. I do not stand over her and that seems to help, but she trys to get up, i just keep putting her back in the same spot and tell her she has to sit because she can not do that to her brother. Maybe u can get a little kitchen timer and set it up and tell ur 2 yr. old not to get up till they hear the ding of the timer. But u need to keep to putting them in time out and not let them think they tell u when they can get up. Dont make abig deal about it but just keep putting him back in time out to let him know that is ur ruling. I know that part of it is the age and part of it is now that my one yr. old is interested in paying my daughter feels like she doesnot want to share or he is not allowed to do what she doesnt want. i just remind her she is not the mommy and he is allowed to do whatever he was doing. I hope this has helped. I know it can be upsetting.....hope things get better for u.
K.